I happen to use IntelliJ Idea 10.5.2 with Scala and SBT plugins to code in Scala on an XUbuntu 11.10 system with Oracle JDK 7.
And I can't close editor tabs with Ctrl+F4 (while right-clicking on a tab shows this shortcut for closing).
Any ideas about the reason probable and a way to fix?
Looks like xfce uses Ctrl+F4 as global shortcut that gets captured before it's propagated to IntelliJ. See this page for how to change shortcuts.
Alternatively you can also change the keybindings in IntelliJ. Use 'File|Settings' and got to 'Keymap' in the settings window. The 'close' action is bound to Ctrl+F4