dummynet pipes

Hello
I have found one thing.
It seems there is some problem in IPFW dummynet.
I use the same ruleset on FBSD 5.1-RELEASE,  5.2.1-RELEASE and -CURRENT.
For example, if I set pipe to 64Kbit I get only half real speed 32Kbit 
on 5.2.1 and CURRENT

example:
 ${fwcmd} pipe 110 config bw 64Kbit/s queue 16KBytes
 ${fwcmd} pipe 111 config bw 64Kbit/s queue 16KBytes
 ${fwcmd} add 6050 pipe 110 ip from not 10.0.0.0/8 to 10.27.10.9 out
 ${fwcmd} add 6055 pipe 111 ip from 10.27.10.9 to not 10.0.0.0/8 in

on 5.1-RELEASE is everything working properly
Please could anybody check this ruleset (or similar) on 5.2.1-RELEASE 
(CURRENT) and 5.1-RELEASE
if it is my mistake or not.
thanks for help.
Jiri