hmh ..someone else had the same problem earlier.
have you tried adding all the stuff inside ID="Toolbar_WebstoreButton" as there's a few tags it includes. could try to set those to width="1" height="1"
check them from
Skin Art Pack / SkinDictionary.txt if none here won't be able to post them.
sorry I don't have those examples here atm as im not on my main pc