Cannot choose apps to share with in Google Play Store
Identified the cause.  

It is known that Xposed clashes with heavily modded stock UI. That's one reason Xposed version 2.5.1 is the last version which supports without breaking theming engine. Xposed has a setting "Disabled Resource Hooks". If you uncheck it, this problem doesn't occur, but if you check it,it recurrs.

In my case, I don't want to uncheck it as it breaks other things in UI, so it's easier to live with the problem. Though why this should only happen with Google Play Store is unexplained