https://bugs.winehq.org/show_bug.cgi?id=56161
--- Comment #2 from Felix jan.felix.muenchhalfen@rwth-aachen.de --- (In reply to Dmitry Timoshkov from comment #1)
This is essentially duplicate of 56122, however this bug report has more details, and a reference to .Net source.
Oh yes, your patch would work with what .net pe loader does there. I have to add to my "bug" that, though MapViewOfFile3 does not down-round, it would not fix this problem because "offset" is also not 64k aligned in the .net pe loader.