How can there be duplicates in an nnml *Gnus Browse Server*

[Julien Cubizolles]

I'm using a nnml named "local" server for all the saved messages I
keep. I noticed that groups (ie directories in ~/Mail/) show up twice in
the *Gnus Browse Server* buffer for this server. I've tried manually
cleaning the ~/Mail/active file but it didn't remove the duplicates.

What data/file is Gnus using to create the list of groups in the *Gnus
Browse Server* buffer ?

Could these duplicates be the reason why some messages marked read in
some of these groups randomly appear new after a while ?

Any help in these matters would be very much appreciated. I've been
trying for years to get rid of this annoying problem.

Julien.