Bestcomm tasks and interrupts on MPC5200(B)

[Dave Best]

I'm trying to write a driver which uses the Local Plus Bus on my MPC5200B and therefore have to use BestComm DMA, which requires me to use a Gen_BD task for data transfer with Local Plus.
I tried to follow the fec driver that is currently used and took a peek at the mpc52xx-ac97 driver which at least uses the same kind of bus as I.

Initialising the task, resetting and enabling works fine. Even request_irq reports no error, but when I start a transfer it hangs and if I am lucky, an interrupt occurs after quite some time. But it's always the BestComm ethernet rx task which produces an RFIFO interrupt, presumably after the watchdog catches on. 
If this happens my interrupt occurs to.

I tried to debug this situation but I am still clueless.
If I use the MPC5200 Interrupt emulation registers to force an interrupt for my interface to occur, nothing happens except that it hangs.

Any hints, tips or help appreciated.

Dave