Steam screenshot function freeze game

Please check the known issues list before posting a bug.
No sign of it I can see

Platform, device version and operating system
e.g. Android, Samsung Galaxy S8, Nougat
PC, custom built gaming desktop, Windows 7

Screenshot or image

What you were expecting to happen, and what actually happened
I was expecting the game to continue to function. Instead, it froze.

How often does this happen? When did it begin happening?
This happened by accident once, and replicated immediately every time I have done it since.

Steps to make it happen again
I press F12 (my key bind for Steam screenshots) and the game immediately freezes. This happens on the map screen and in battle. We actually lost a Pet Gnome to this. (I was up against a clan mate in Arena, so I took a screenshot - sadly after I killed the pet gnome, so no proof - and afterwards I tested in normal PvP and on the map screen.)