Not necessarily. Could be a problem with passing 64-bit values to varadic functions generally. I could definitely imagine this happening on a 32-bit platform.

This has bitten me on QNX. I was porting UQM for fun, and it was failing when entering a dialogue,

Turns out, on QNX you can't pass short int into variadic function, which is expected behavior as far as C is concerned (you should only pass int or full size types), but it worked on every other arch so it took me a while.

The generated assembly was garbage, so I assume it was a compiler bug. It also got fixed in later revisions, but since the compiler is shipped with the CRT... :)

I don't actually recall if we were using the shipped CRT or not, I'm guessing only minimal parts of it were used, if any, since embedded projects tend to write their own subset of the needed standard library functions.