Default Printer changes - Users terminal server

I have three 2008 terminal servers and they are 64 bit running fairly well.

We have some users that call up saying that there default printer keeps changing.

We have one local printer on all the TS's ... and that is PDF Creator, rest are network printers

So sometimes when they log into the TS their default printer changes to the PDF Creator.

It's not a printer on the 'local' computer so it's not being redirected
It doesn't happen all the time
I have made fully sure that they are logging off and not disconnecting the session.

any tips ?