"runs on an intel-chip"

What intel chip? - that could include an 8051!

Don't forget that the sizes of int and long are target-dependent; also, for >8-bit objects, I think Keil uses the opposite byte ordering from other intel chips.

What sort of "Strange" things are you seeing?

Don't forget that you have to be very careful with printf in C51 - if you're basing your observations on printf output, that could be your problem. Read the Keil manual very carefully - there's a section specifically on problems with printf - and try a search on the Keil site.