[Zope] FSCounter fills up undo log

Hi, I installed FSCounter 1.2 on my Zope 2.3.3 (linux Debian potato). Calling a FSCounter instance via <dtml-var counter> from index_html document fills up the undo log with one entry per request. After a while there are hundrets of these entries in my undo log which lets the data.fs growing up very rapidly. Any ideas? Thanks Marcus