[otrs] Broken item in the Navbar

At some point during our life of OTRS, we seem to have gained an Item into our navbar with no description etc. It appears between the 'Logout' and 'Preferences' items, and is just a broken image with an ALT tag full of junk code. Looking at the page source, there is an unterminated string constant in the html, resulting in a lot of perl markup being dumped into the ALT tag. I've traced this into the .dtl and I can see the Item block code which is responsible, but I've trawled through our config files and I cannot find a navbar entry that has null descriptions/names. Has anyone else seen this, or can provide any insight on how to debug the system to find out an entry in the config which is feeding this item? many thanks