Just so we have another data point, I am using m0n0wall 1.3b5
with traffic shaper and have not experienced the locking problem.
I should note that I am not using captive portal, the firewall rules
are to allow all traffic both ways, and NAT is completely disabled.
The traffic shaper also does not have any queues defined and just
one pipe with rules to simulate a bad low bandwidth WAN link.
Seems to work just fine for that.