problem with ERR_ZERO_SIZE_OBJECT

Hi,

I have a problem with Squid's ERR_ZERO_SIZE_OBJECT error. I googled and
looked into Squid's source code. Looks like only when remote server closes
the connection without sending any data causes an ERR_ZERO_SIZE_OBJECT.

My case is I have multiple Squid processes running on servers which are
geographically distributed. Squid processes only communicate with each
other. So my question is what could cause Squid close a connection to its
"client" (which in my case is some other Squid process) without sending
any data?

BTW, I'm using Squid 2.3 but I also checked code of 2.5 and found no clue
either.

-- 
Chengdu