Comment 12 for bug 1244090

This has gotten even more annoying in 14.04, though my problem is a tad specific.
I have set the keyboard shortcut “Switch to next source:” to Left Shift+Right Shift (used to be X server's default). However this have an interesting side effect in some cases: now just pressing (one) Shift key to write an upcase letter also causes a temporary lose of focus, effectively breaking some text fields – like a Twitter's compose and reply boxes mentioned by kolen. Reverting back to the default Super+Space solves this issue, even switching the keyboard on Twitter doesn't lose the focus.
So apparently some shortcuts may have an unintended side effects.