We all know the “Zellweger” mystery of episode 525 “Top of the heap”.

A short excursion 15 years back in time:
Renée Zellweger was credited in this episode but she never appeared in any episode of MWC.
How could this happen?
Nobody knows, but I think that someone (“one someone” who was in charge for the credits) saw “Joey Lauren Adams” and thought it was Renèe Zellweger – they realy look very similar.
But this doesn’t explain why “Joey Lauren Adams” was credited for her role as “Mona Mullins” too – which of course this is correct.

Back in 2006 Sony – just a few days ago – has released a press release for season 5.
Here is a short excerpt:

[...]Al becomes the neighborhood stud, Bud gets into a car accident, Peg takes up ballroom dancing, and the hapless Marcy (Amanda Bearse) marries handsome con artist Jefferson (Ted McGinley of TV’s “The Love Boat,” “Happy Days”). Guest stars this season include Pamela Anderson (TV’s “Stacked,” “VIP,” “Baywatch”), Matt LeBlanc (TV’s “Friends,” “Joey”), Academy Award®-winner Renee Zellweger (Cold Mountain, Chicago, Bridget Jones’s Diary), Joey Lauren Adams (Chasing Amy),
[...]

And looks how’s announced again !!
15 years after episode 525 the mythos Renée Zellweger is still alive.

Here is a picture with Joey Adams in episode 525 and Zellweger/Adams in other movies.