Huh.  Something is behaving different between the L shoulder button and the shift on the keyboard.
Press Fn-L-,
That is, Fn+Left shoulder+comma.
Oh yeah! The keyboard matrix can only handle 2 keys at a time.  When you press the third one, it's probably getting confused.  The shoulder and game buttons are their own GPIO lines so have no such restriction.
edit: Oh duh! The problem isn't the keyboard limit, the problem is that Fn-Shift is caps-lock.  Just tried this and it works: press and hold shift, THEN the fn key, then the , button.  Works every time.  Pushing the Fn button first it turns the shift into caps lock.