I use Ctrl-F12 a *lot* in IntelliJ IDEA, so it was annoying when I
started work on a new desktop with Xubuntu and found that it wasn't
working anymore. The IDEA settings were all there, but it wasn't
getting picked up.
Contacted support and found out the problem is due to conflict with
Xubuntu default keyboard mappings.
Xubuntu maps Ctrl+<function key> to Switch Workspaces.
Just go into Settings -> Settings Manager -> Window Manager -> Keyboard (tab)
Go down to Action = Workspace 12 and remove the keyboard mapping.
In the unlikely event you *do* need to move between 12 workspaces,
just map that to another combo, or change the IntelliJ mapping to
something similar like Windows + F12.