Ah, I see your bug.
I am on a case-sensitive file system — which is totally supported by Apple. The file present has "MAC" in it, and the dialogue has "Mac" in it.
Don't feel bad… it took three years of continuous bug reports before Adobe made their case consistent within their applications!
I suggest you should test on the most constrained case, in this case, on a case-sensitive file system. 
I think the other problem I'm having may be related to this, as well.
But you won't even hear about this until Sketchucation takes this message out of moderation status… 