Expiry not working anymore for nnml?

[Bjorn Halvor Solberg <bhso@pacbell.net>]

For my nnml:misc group, I have no group parameters save for formatting
the line:

((gnus-summary-line-format "%U%R%z%~(form (gnus-extra-header 'To))@%~(cut-left 2)~(max-right 6)~(pad 6)o %I%(%[%4L: %-20,20f%]%) %s\n"))

However, as of about a month ago, Gnus stopped  deleting the articles I
have ticked as expirable ("E") after a week like it used to do, and like
the info says it should do:

" To make Gnus get rid of your unwanted mail, you have to mark the
articles as "expirable".  This does not mean that the articles will
disappear right away, however.  In general, a mail article will be
deleted from your system if, 1) it is marked as expirable, AND 2) it is
more than one week old."

I see the same behaviour for my other nnml groups as well, and I'd
appreciate some pointers to where to look for the a solution to the
problem, or a solution if anyone else has experienced this.  Currently
I'm using Emacs-20.4.1 and pgnus-0.96.

Thank you in advance,

Bjorn.