So I've noticed that often times the shop won't let me buy items or even close it via the X in the upper corner. Half the time I have to hit the esc key to get rid of the shop menu and re-open it.
I don't know what causes it, but the shop is extremely buggy for me.
With today's PBE deploy, a fix for this (or most of these) should be active.
If you have played after you have patched with today's patch and have had severe unresponsiveness within the item shop occur to you, please respond to this thread with under what conditions you reached that point.