Thank you for your detailed answer. I didn't repeat your tests but this seems like a good explanation.

Yes, unchecking "Has Exit Time" and using a condition instead will work. I mentioned this already in my question in the "Workaround" section.

Thanks for the details, but I still don't understand why an exit time of 0 doesn't cause an immediate transition. According to the definition here, shouldn't a 0 exit time mean that on the first frame where 0% of the animation has played, the Exit Time condition should be true?