seeing pf: state key linking mismatch! with pf on up to date current but not on FreeBSD 7.4-STABLE

[eculp]

Something is strange with PF.  I get the above error using pf on  
current but not on FreeBSD stable.  The pf configuration hasn't  
changed for a couple of years on either and they are the same except  
for hardware names.

The two machines are:
9.0-CURRENT FreeBSD 9.0-CURRENT #247: Wed Jun 29 04:49:16 CDT 2011
7.4-STABLE FreeBSD 7.4-STABLE #1228: Sat Jun 25 04:42:55 CDT 2011

Anyone else seeing this?

Thanks,

ed