ALT + TAB Doesn't Work (Linux Mint MATE)

Somehow (I have no idea how) I broke my ALT + TAB functionality. I'm using Linux Mint (MATE edition), and when I press ALT + TAB instead of switching to another application it very briefly shows the desktop, then returns me back to the application I was on. I've tried enabling and disabling both the "Application Switcher" and "Static Application Switcher" in the CompizConfig, but neither has any effect. Even if both are disabled, I still get the same "briefly show the desktop then return to the original app" behavior. This made me think that I somehow had rebound my ALT + TAB keybinding, but when I go to Keyboard Shortcuts it does show "Move between windows, using a popup window" set to ALT + TAB. If I change it (eg. to CTRL + ALT + A) the "show desktop briefly" behavior goes away ... unless I then do CTRL + ALT + A, in which case that behavior returns. So in summary: * I have a keybinding for ALT + TAB to "Move between windows, using a popup window", and this binding appears to trigger the "show desktop briefly" behavior even if I change it to a different binding * I previously had "Static Application Switcher" enabled in CompizConfig, but whether I enable it, "Application Switcher", or none of the above, I see the same behavior Thus, it seems I've somehow actually broken the "Move between windows, using a popup window" functionality, completely independent of Compiz ... and I have no idea how I can restore it. Does anyone have any suggestions?