2.6.19.1 bug? tar: file changed as we read it

Trying to backup up a filesystem mounted via CIFS, I got these messages
from tar:

tar: t/2.6.10-orig/net/ipv4/netfilter/ipt_CONNMARK.c: File shrank by 1178 
bytes; padding with zeros
tar: t/2.6.10-orig/net/ipv4/netfilter/ipt_TCPMSS.c: File shrank by 4177 bytes; 
padding with zeros
tar: t/2.6.10-orig/net/ipv4/netfilter/ipt_DSCP.c: File shrank by 1172 bytes; 
padding with zeros
tar: t/2.6.10-orig/net/ipv4/netfilter/ipt_tos.c: file changed as we read it
tar: t/2.6.10-orig/net/ipv4/netfilter/ipt_ECN.c: File shrank by 1638 bytes; 
padding with zeros
tar: t/2.6.10-orig/net/ipv4/netfilter/ipt_mark.c: file changed as we read it
tar: t/2.6.10-orig/net/ipv6/netfilter/ip6t_mark.c: file changed as we read it

This was with kernel 2.6.19.1 SMP on x86_64, creating a tar file on a local
jfs filesystem (t is the source path on a cifs mount.)

Using 2.6.18.6-pre2 uniprocessor i386, with smbfs instead of cifs, everything
works fine so I'm pretty sure the server is OK.

Does this match any known problems?

-- 
MBTI: IXTP