packet filter problem on transparent firewall using bridge and pf

[ProAce]

I have another problem .....   >_<

Sometimes , I cannot connect to server ( in trust zone ) from untrust.
Even I turn off the firewall, the situation still come up.

But, when the state appears, I ping some ip from the server ( in trust
) to a host ( in untrust ).
Suddenly, I connect to the server ( in trust zone ) successfully from
untrust at this time.

Why？How can I solve the problem？