Do you print your shipping labels through Ebay? If so, then the default insurer is not the USPS themselves it is a third-party called ShipCover. ShipCover increased their prices effective October 1st.
If you would like to read more about it there is some discussion on the Ebay community chatboards...
http://forums.ebay.com/db1/topic/Pac...ice/5100109852
http://forums.ebay.com/db1/topic/Pac...ver/5200109391