There's always going to be some conflicts in one manner or another - take abilities, for example. You can't use the QWER abilities while the shop is open. Is this a bug, or just a prioritizing feature? I sometimes want to use an ability to get a speed boost and start leaving the base while I'm finalizing that purchase - you know - to get back out to the battle quickly. But because of the prioritizing, I have to purchase, then close the shop, THEN use the ability.
I'm sure some people would complain that it's a bug, but what sort of repercussions would come from allowing the chat or abilities while in the shop? There would probably be some issues with searching for items, etc.
That being said, the idea of clicking on the shop UI to put focus on it and allowing chat / abilities up until that point could possibly work. However, since I don't have knowledge of the inner workings of the code, I really don't know how that would affect the rest of the aspects of the shopping experience. Having worked in Software Development for many years, I've seen plenty of examples of adding a new "feature" introduce multiple bugs elsewhere.
Caveat emptor - and be careful what you wish for!