Well this is embarrassing.
I refused to believe that there could be that much difference as I've extensively tested UltraRes in the past. So I just ran some tests and, sure enough, there was a difference. Turns out UltraRes has been broke since Version 16.03. We made some code optimizations and moved some stuff between stack and heap and missed a variable.
Sooooo... Version 18.07 will coming soon.
It's called human error for a reason. I'm pretty sure that even Steven Hawking has had some "ooops" moments as well. ;-)