Memory behaves strangely between 0x500 and 0x7C00, but not in Bochs

I have written a lot of code that is loaded from a disc at address
0x500, this code worked like it should most of the time but now I
encountered an error that seems to have to do with corrupted memory:



mov ecx,ModuleData				;ECX contains the offset in ModuleData

add ecx,0x00000008
mov eax,dword[ecx]
cmp eax,0					;If there are no module dependencies
jz NEAR .checkGroupDeps			;skip module checking



Where ModuleData resides at 0x1274

The problem is: in Bochs it jumps (like it should do in this case) but
on real hardware it doesn't (with Microsoft's Virtual PC - it's the
same story... it doesn't jump either). The value's aren't simply
zeroed out in Bochs... I checked that the data on my CD was really
loaded by looking at the values around this dword. Does anyone know
what could reside at these addresses... after the IDT and BIOS-data
that should go up to 0x500? Remember that most of my code loaded at
0x500 does work... there's only this problem at 0x1274 (or maybe more
to come...).