ast_waitfor_nandfds Warnings


since upgrading to Asterisk 1.2 I always get these warning messages at the beginng of a call:

Aug 20 02:16:47 WARNING[21381]: channel.c:1602 ast_waitfor_nandfds: Thread 229390 Blocking 'CAPI/ISDN1/0456726756-0', already blocked by thread 0 in procedure (null)

I can’t find anything on this.
What’s this?
Can I ignore it?
Or even better (I hate warnings in productive set up environments!) how can I adjust Asterisk to not make these warnings any more?

Thanks in advance,