Not so much a bug, more of an overlooked problem.
I wanted to try out the Luxury Towers talent that I recently earned. It is nice, but it will be more useful later on in the game. The problem is that now I can't deselect it. I can only choose an alternative talent from the same tier, which is increasingly difficult to achieve now that I am stuck with towers costing 100 gold each!
I am playing on android, so I don't know if this issue also exists on the PC version.