First, this is not a new comment, just moved from above.
The use of "one problem case WAS..." WAS/IS a little weak -- it suggests that I WAS at least hoping it was fixed.
After my recent walks through the code, I'm now thinking that it is still probably broken -- maybe it works if you have some kind of alias for max(y) and that threw me off? or maybe I still don't completely understand. 
It'd probably worth it to add a test case and clarify the comment.
Anyway, it was not my intent to change/fix any visible behavior in this change set.