in reply to A Win32 new Perl build dilemma
Try using WinAPIOverride to see if there's any difference in WinAPI calls between the old and the new Perl? If there isn't any, it must be somewhere else (flags in the EXE itself set by the linker? something fishy in the manifest?). If you do find something, it could be traced to the CRT and Perl's use of it.
In Section Seekers of Perl Wisdom