WebShield (ashwebsv.exe) does not scan upload traffic (outbound), only inbound.
Maybe some Java component is downloading something… at the same time… difficult to say.

Here, Lukas shows how to get the ashWebSv.exe dump:
http://forum.avast.com/index.php?topic=27375.msg223114#msg223114

You might want to try running this tool: http://public.avast.com/~rypacek/userdump.exe
When the problem appears please start it with the following command:

userdump ashwebsv.exe

It will create a memory dump of running webshield process (in the file ashwebsv.dmp). Please upload the file to the ftp server (ftp://ftp.avast.com/incoming) or send him a mail about it.