My.yahoo.com

I am using Squid 2.5STABLE4 on Redhat linux as a transparent proxy. Its
actually a Mikrotik.com box that bundles Linux and all this together.
Anyway, I have users complaining about not all of there My.yahoo.com start
page coming up and other times it gives an error of: "Zero Size Reply".
Whats strange is I can log into my my.yahoo account on there PC and it works
fine. They log in with there username and just the top portion of the
webpage shows up. Disabling the cache makes all these problems go away.
When they log on with there cable modem at another location that uses a
cisco based cache it works fine.

Any idea's whats wrong?

Matt