xPL bridging loop prevention

["Mark Hindess" <xpl@xxxxxxxxxxxxxxxxx>]

A little while ago, when I asked about bridging subnets, Mal was kind
enough to point me at an xPL hub for .net.  I took a quick look but
didn't grab a copy and it's disappeared now.  I feel stupid not grabbing
it while I could because it might have helped me answer my current
question.

I've decided I definitely do need to bridge some packets.  (At least,
OSD messages to the wifi Fujitsu tablet PCs I'm putting on a couple of
walls in my house.  So I started writing a bridge to test out my Perl
code.

I hit a slight problem.  I started doing the obvious things to prevent
loops using a simple cache of hashes of messages the bridge has seen,
but it catches some packets that it shouldn't.  Specifically if someone
sends two identical x10 bright messages in quick succession, they have
the same text in them and so their hashes match and the second is
suppressed and lights remain dim.  ;-(

I'm a bit stumped as to how to handle this correctly.  Anyone know how
the .net version handled this problem?  Or have any suggestions?

Regards,
Mark.