I'm assuming once per short rest is intentional though I guess you could try reporting it as a bug to Larian to see if you can get confirmation.

I'd disagree it makes it useless, at least for me given I don't tend to use it multiple times a day anyway. Out of interest, how do you use it such that once per short rest isn't useful?

"You may call it 'nonsense' if you like, but I've heard nonsense, compared with which that would be as sensible as a dictionary!"