Ctrl, Alt and arrows keys cause character deletion

I am using the sidewinder keyboard with Plover 2.1.2 on Ubuntu Maverick. When I use Ctrl, Alt and arrow keys to change workspaces while using Plover, a character in the text which is currently focused is deleted, namely the one to the left of the cursor. I have tested this further and it appears that Ctrl, Alt, Super(windows key) and the arrow keys are acting like Backspace, except that 'Up' moves the cursor up and then backspaces, and 'Right' appears to delete to the right (though it may be moving right then backspacing, which would be more consistent).

This may be intended behaviour, but it may not be expected by beginners.