border-only ghost window blocking mouse clicks

At some point (I don't remember when it started), some kind of ghost window appeared that only has a border (displays as rounded but behaves as rectangular), blocks mouse clicks, and won't disappear when I minimize all windows. What might this be, what might have caused this, and most importantly, how might I be able to get rid of this? Here is some additional information that might help diagnose the issue: - This does not seem to affect the lock screen. - The behavior with the Alt-Tab window switcher is very strange when I click on a window: - If the I click outside the ghost window, it immediately switches to the window I clicked on. - If the I click inside the ghost window, it immediately closes the window switcher, but doesn't open the new window until I move my mouse outside the ghost window. The final position of my mouse doesn't seem to matter. - I'm using Xfce version 4.18 with GTK version 3.24.37, as part of Debian GNU/Linux 12 (bookworm). - I have xserver-xorg version 1:7.7+23 and xserver-xorg-core version 2:21.1.7-3. - The panel at the top of my screen doesn't respond to mouse clicks, but the data it displays does update, and the apps menu works when I activate it with a keyboard shortcut. - Here is the output of xwininfo -d :0 -all after clicking on the ghost window:

xwininfo: Window id: 0x1b75612 "xfce4-panel"

  Root window id: 0x6d1 (the root window) (has no name)
  Parent window id: 0x6d1 (the root window) (has no name)
     1 child:
     0x1b75613 (has no name): ()  1x1+-1+-1  +2926+461

  Absolute upper-left X:  2927
  Absolute upper-left Y:  462
  Relative upper-left X:  2927
  Relative upper-left Y:  462
  Width: 328
  Height: 637
  Depth: 32
  Visual: 0x6ba
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x1a00002 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: yes
  Map State: IsViewable
  Override Redirect State: yes
  Corners:  +2927+462  -585+462  -585-341  +2927-341
  -geometry 328x637+2927+462

  Bit gravity: NorthWestGravity
  Window gravity: NorthWestGravity
  Backing-store hint: NotUseful
  Backing-planes to be preserved: 0xffffffff
  Backing pixel: 0
  Save-unders: Yes

  Someone wants these events:
      KeyPress
      KeyRelease
      ButtonPress
      ButtonRelease
      EnterWindow
      LeaveWindow
      PointerMotion
      ButtonMotion
      Exposure
      VisibilityChange
      StructureNotify
      FocusChange
      PropertyChange
  Do not propagate these events:
  Override redirection?: Yes

  Window manager hints:
      Client accepts input or input focus: Yes
      Initial state is Normal State
      Window type:
          Popup Menu
      Process id: 2661 on host 

  Normal window size hints:
      Program supplied minimum size: 328 by 637
      Program supplied maximum size: 328 by 637
      Program supplied base size: 0 by 0
      Program supplied window gravity: NorthWestGravity
  No zoom window size hints defined

  No window shape defined
  No border shape defined

- Here is the output of xwininfo -d :0 -all after clicking on the panel at the top of the screen:

xwininfo: Window id: 0x1a00003 "xfce4-panel"

  Root window id: 0x6d1 (the root window) (has no name)
  Parent window id: 0x1200587 (has no name)
     4 children:
     0x1a0000e (has no name): ()  90x50+1190+0  +3750+416
        1 child:
        0x2800003 "wrapper-2.0": ("wrapper-2.0" "Wrapper-2.0")  90x50+0+0  +3750+416
           1 child:
           0x2800004 (has no name): ()  1x1+-1+-1  +3749+415
     0x1a0000d (has no name): ()  69x50+1121+0  +3681+416
        1 child:
        0x2600003 "wrapper-2.0": ("wrapper-2.0" "Wrapper-2.0")  69x50+0+0  +3681+416
           4 children:
           0x2600029 (has no name): ()  22x22+24+1  +3705+417
              1 child:
              0x1c00003 "xfce4-power-manager": ("xfce4-power-manager" "Xfce4-power-manager")  22x22+0+0  +3705+417
                 1 child:
                 0x1c00004 (has no name): ()  1x1+-1+-1  +3704+416
           0x2600019 (has no name): ()  22x22+0+26  +3681+442
              1 child:
              0x3000003 "Ethernet network connection “Wired connection 1” active": ("nm-applet" "Nm-applet")  22x22+0+0  +3681+442
                 1 child:
                 0x3000004 (has no name): ()  1x1+-1+-1  +3680+441
           0x260000a (has no name): ()  22x22+0+1  +3681+417
              1 child:
              0xc00010 "IBus Panel": ("ibus-ui-gtk" "ibus-ui-gtk")  22x22+0+0  +3681+417
                 1 child:
                 0xc00011 (has no name): ()  1x1+-1+-1  +3680+416
           0x2600004 (has no name): ()  1x1+-1+-1  +3680+415
     0x1a0000c (has no name): ()  254x50+695+0  +3255+416
        1 child:
        0x2400003 "wrapper-2.0": ("wrapper-2.0" "Wrapper-2.0")  254x50+0+0  +3255+416
           1 child:
           0x2400004 (has no name): ()  1x1+-1+-1  +3254+415
     0x1a00004 (has no name): ()  1x1+-1+-1  +2559+415

  Absolute upper-left X:  2560
  Absolute upper-left Y:  416
  Relative upper-left X:  0
  Relative upper-left Y:  0
  Width: 1280
  Height: 51
  Depth: 32
  Visual: 0x6ba
  Visual Class: TrueColor
  Border width: 0
  Class: InputOutput
  Colormap: 0x1a00002 (not installed)
  Bit Gravity State: NorthWestGravity
  Window Gravity State: NorthWestGravity
  Backing Store State: NotUseful
  Save Under State: no
  Map State: IsViewable
  Override Redirect State: no
  Corners:  +2560+416  -0+416  -0-973  +2560-973
  -geometry 1280x51-0+416

  Bit gravity: NorthWestGravity
  Window gravity: NorthWestGravity
  Backing-store hint: NotUseful
  Backing-planes to be preserved: 0xffffffff
  Backing pixel: 0
  Save-unders: No

  Someone wants these events:
      KeyPress
      KeyRelease
      ButtonPress
      ButtonRelease
      EnterWindow
      LeaveWindow
      PointerMotion
      ButtonMotion
      Exposure
      VisibilityChange
      StructureNotify
      FocusChange
      PropertyChange
  Do not propagate these events:
  Override redirection?: No

  Window manager hints:
      Client accepts input or input focus: Yes
      Initial state is Normal State
      Displayed on all desktops
      Window type:
          Dock
      Window state:
          Sticky
          Skip Pager
          Skip Taskbar
          Focused
      Process id: 2661 on host 
      Frame extents: 0, 0, 0, 0

  Normal window size hints:
      Program supplied minimum size: 1280 by 51
      Program supplied maximum size: 1280 by 51
      Program supplied base size: 0 by 0
      Program supplied window gravity: StaticGravity
  No zoom window size hints defined

  No window shape defined
  No border shape defined

Here are some screenshots to illustrate how it behaves as I change display settings. It's not really visible in the thumbnails; click on them to see the full-size versions.