XFCE Focus/Event Handling

In XFCE I defined Ctrl+Shift+Space to open the system menu. After installing Intellij I noticed that it uses that shortcut in a useful way. However, if I press it the system menu pops up. This is confusing to me since the application has the focus and the key events should be caught by the application before the OS consumes it. In other words, the OS should be the last resort. How do I make XFCE work my preferred way? If it can't, which window manager can do that and isn't that much different to XFCE so I don't have to relearn everything? _A [similar question](https://stackoverflow.com/q/21497412/483113) has been asked, but didn't receive much attention and is also already 30 months old..._