ipmasq not letting through all web sites?

["Marc Sherman" <msherman@myrealbox.com>]

I just installed the ipmasq package, and hooked up my
win98 box through my linux machine.  The linux machine
has 2 ethernet cards, eth1 is connected to the local
net (the Windows machine), eth0 is connected to an
ADSL line using PPPOE.

On the Windows machine, I can hit some web sites, but
not others.  On the linux machine, those same websites
work fine in lynx.  For example, www.sjgames.com works
on both machines, while www.sciplus.com only works
on the linux box.

My ISP (Bell Sympatico) has a "transparent" caching
proxy server installed on port 80; I suspect that that
may be the cause of the problem.  When I explicitly
specified a proxy server in IE5 on the windows machine,
some web sites that failed before started working
(like the eservice.sympatico.ca site on Sympatico),
but others (like www.sciplus.com) continued to fail.

If the proxy server is messing with the returned
http data so that my ipmasq rejects the packet, is
there any way I can get ipchains/ipmasq to log the
rejected packet so that I can figure out how to
avoid this problem?

Thanks,
- Marc