I don't see any explicit affirmation in the datasheet that VDD1 and VDD2 are completely independent.
I tried VDD1=3.3V, VDD2=5V on the bench and everything seemed fine. But in our application both VDD1 and VDD2 are not set in stone and might change later. Most likely VDD1=1.8V and VDD2 somewhere between 3 to 5V (referred to two different grounds obviously). But I can't anticipate every possible scenario. Can I safely assume that:
Mea culpa I did not RTFD (read the fabulous datasheet) closely enough. Thanks