"got bad cookie" warnings/errors?

Hi gang,

I've been seeing lots of these lately:

got bad cookie vp 0xc2f40b68 bp 0xc929a1e8
got bad cookie vp 0xc318d124 bp 0xc91d4240
...

I grepped around, and it seems it has something to do with NFS (well, I found 
this being printf'ed in src/sys/nfsclient/nfs_bio.c

I have two NFS machines from which I mount, a 4.8-STABLE machine and a NetBSD 
1.6.1 box. I haven't seen any dataloss or panics. But still, should I be 
worried? How serious is this message?

I'm running a very recent CURRENT, cvsupped this week, and a kernel wih 
Soeren's ATAng patches (which seem to work very well).

Cheers,
Emiel