Peter,
I've had a similar experience. I'm using obsd 3.5-release and building my first pf.conf file. I found this afternoon that in fact synproxy was causing things not to work, while if I changed it to modulate or keep things worked just fine.
Unfortunately nothing was logged when synproxy was not working, which drove me nuts. I had tcpdumps going on just about every link the packets were traversing. In a fit of desperation I replaced synproxy with modulate and things started working. Changed it back and it broke again.
I feel better now. I was starting to think that I'd lost my mind. I was looking at the rules and thinking this has to work, yet it would not, yet no log of drop. Considering my default policy is block drop I should have seen something.
-Chad-
