You cann't reply to messages if transperant web proxy is turned ON. Anyone have sugesstions to stop cacing mail.yahoo.com?

Seems that web-proxy is clearing some data from HTTP header:
the request:
POST /ym/Compose?box=%40B%40Bulk&Mid=6166_1654_22_1763_6_0_2_-1_0&inc=&Search=&YY=19819&order=down&sort=date&pos=0&view=a&head=b HTTP/1.1

comes to:
POST /ym/Compose? HTTP/1.1