MPC8xx Debugging: function call vs. no function call

Hello,

I am not yet pretty familiar with 8xx system programming, so maybe you could give me some debugging hint. My C code which programs the the CPM (USB) has to execute the following commands:

   eieio();
   usbregs->usb_uscom = 0x80 | 0;
   mb();

If i put those instructions in an new function, the CPM behaves as wished, elsewise it depends on the remaining code. E.g. the number of NOP machine code instructions before make a difference:

1.)
...< remaining C function code>
__asm__("nop\n\t");
eieio();
usbregs->usb_uscom = 0x80 | 0;
mb();
... <other code>

2.)
...< remaining C function code>
__asm__("nop\n\t");
__asm__("nop\n\t");
eieio();
usbregs->usb_uscom = 0x80 | 0;
mb();
... <other code>

Every hint howto find my mistake is appreciated! Thanks Josef