I wondered if anyone has seen this behavior in Photoshop. Double listings for Extract, Liquify and Pattern Maker. I've had this happen on several occasions, but I have no idea what the cause might be.
Everything still functions normally, just double listings.

Never had it happen to me. However, have you upgraded Windows operating systems or re-installed PS? Between different version of PS and Windows, filters, preferences, and user settings were stored in different locations. Everything used to be in C\Programs\Adobe\Photoshop sub folders (filters, presets, etc). Newer versions are in the Documents & Settings common settings folder. I would think that on start up PS may be seing the same filter appear in two folders or there are actually two versions of the same filter in one folder.
Regards, Murray

I can also say i havent had it happen to me, although i have had a couple of things go strange on me when i changed to vista

Palms

Yes, I have had this problem when extracting/adding new filters that were downloaded!

The filters are in another folder besides Photoshop only>filters

look in the "Photoshop only>filters" folder to get the proper name for the duplicated filters and/or do a search for the duplicates.. If they are duplicated in the array of Photoshop folders then either delete them, move them into a non use folder, rename and put an ~ at the beginning of the filter name (~Extract.8BF (making it invisible))

I had it happen. It's because photoshop is looking in another place due to a previous install of another version.