I just want to report that this bug still appears valid in 4.12.1 as found in stretch.
My impression is that only shortcuts involving the <Super> key are affected. In particular I have set Ctrl+Super+Up/Down/Left/Right as Shortcut for Upper/Bottom/Left/Right Workspace . I made the following observation: Pressing accidentally Fn+Ctrl+Left/Right/Up/Down deletes only the Ctrl+Super+Left/Up functions.
