When attempting to bind some keys (mainly I was clicking on them to see if it gave info or a tooltip as to what some were) I pressed ESCAPE to back out of binding it.

 

It told me Escape was already bound, so I clicked cancel.

 

Then, underneath that was an unclickable warning dialog asking me about saving the changes. I had no option but to ALT-F4 the client.

 

I believe the key here is I had just started up the game, so my Always Save was equal to "No" still. And the underlying UI is trying to move back a page from me pressing ESCAPE, plus providing the rebinding warning simulatenously... locking things up.

 

Progression of pics below is sequential for you--- 

Still present in 1.05