Sorry, I delayed investigating this problem for much later, when I have 32-bit version of my engine running many real tasks without glitching or crashing.

Add to that I install my own SEH handler for Win32, which I had to change to VEH handler for Win64...
Add to that that I use pointer arithmetics in many places and had since weeded out several coding horrors via simple search for "cardinal" keyword...
No, this was probably stupid me crying wolf because of trashed memory elsewhere