a5 referencing in a ff-environment

[tkunze@mvax.kgw.tu-berlin.de (Tobias Kunze)]

I can now be more specific about the problem i have: for some obscure reason, 
_some_ of my c written functions don't get the address value that the ff-env structure stores in its a5-ptr slot supplied as their a5 register value through which they reference their data.
I have an initialization routine which sets up all in the data area (negative offsets from this a5-ptr value) and everything is ok there, but after that, it seems that all other functions use the normal, that is, mcl's a5 value.
I have _absolutely_ no idea what goes wrong there and would appreciate any hints.  Did anyone experience similar difficulties?

Thanks, 
Tobias