Well, if your offset was a "signed byte" then -1 would actually be passed as 254. So Blitz may be using "signed integers" or "signed longs" for that, and -4 would be some positive value after compiling.
This *could* (I'm guessing here) explain the problem on integrated chipsets, the onboard video probably uses the top memory area as VRAM, and then this would actually be writting/reading from there...
This *could* (I'm guessing here) explain the problem on integrated chipsets, the onboard video probably uses the top memory area as VRAM, and then this would actually be writting/reading from there...