Sorry for the terrible bump, figured it'd be better than opening a new one about it..
I purchased Construct 2 Personal Edition few days ago, and I'm encountering the same "open capx file" issue... While others reverted to using the non-steam edition, I can't do that, since I don't have a license file after purchasing it from Steam...
Any news about this issue?
There are a few work-a-rounds, but I don't see this issue being resolved by steam anytime soon. They pretty much said to me - they don't care.
I had endless issues with steam version over and above broken file association, and moved to the stand-alone version. Best thing that ever happened.
I also have since not purchased any software from steam based on my experience with them over issues. Games yes, software, never again.