Message Filterse Not Saved

When I create a message filter they are never saved so when I look in the Filter list it has disappeared.
I've checked the Data\profile\Mail sub folders and a msgFilterRules.dat file is created but is blank.
Occasionally, the message rule is saved in the file, but does not appear in the Message Filters list box the next time TBird runs. Despite not being in the list the rule runs automatically when downloading email!
Any ideas what's going on!

(Tbird 2.0.0.18, TBird Portable 0.9)

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I've worked out what's going on.
The filters only get saved if you open a message and then right click on an email address in the header, select 'create filter from this email', create the filter and ok it.
The Data\profile\Mail\Local Folders\msgFilterRules.dat gets updated and magically the fully populated filters list appears.
If you view the list from Tools - Message Filters the list does not get populated.
Weird!
Anyway it's well wroth backing up Data\profile\Mail\Local Folders\msgFilterRules.dat just in case TBird resets all the filters.