fingerprinting / pf and return-rst

[glaive_(_at_)_vaned_(_dot_)_net]

the reset packet returned by a "return-rst" rule in pf differs slightly
from a regular reset packet on a non-listening port (namely pf does
not set dont fragment)

is this behaviour known?  i apoligize if this has already been
brought up, i did not see it in the lists.  the machine is
running -current from a couple weeks ago.

non-pf
1.2.3.1.6787 > 1.2.3.5.49: S 3096013632:3096013632(0) win 16384
<mss 1460,nop,nop,sackOK,nop,wscale 0,nop,nop,timestamp 252827829 0> (DF)
[tos 0x10]
1.2.3.5.49 > 1.2.3.1.6787: R 0:0(0) ack 3096013633 win 0 (DF)

pf return-rst
1.2.3.1.10814 > 1.2.3.5.50: S 3492113667:3492113667(0) win 16384
<mss 1460,nop,nop,sackOK,nop,wscale 0,nop,nop,timestamp 252827864 0> (DF)
[tos 0x10]
1.2.3.5.50 > 1.2.3.1.10814: R 0:0(0) ack 3492113668 win 0

regards