bug#20610: 25.1.1 Gnus fancy mail splitting not working anymore

[Gijs Hillenius <gijs@hillenius.net>]

Trying out Debian's Emacs25, (GNU Emacs 25.1.1 (x86_64-pc-linux-gnu,
GTK+ Version 3.22.1) of 2016-10-11, modified by Debian)

I notice that my fancy split using bbdb is no longer working, similar to
what Sebastien Vauban noticed last year.

In the server buffer, this is how the mail server is configured

(nnimap "thuis"
	(nnimap-address "server")
	(nnimap-inbox "INBOX")
	(nnimap-split-methods nnimap-split-fancy)
	(nnimap-unsplittable-articles
	 '(%Deleted %Seen))
	(nnir-search-engine imap)
	(nnimap-stream tls))

Which works in Emacs24.

here is a shortened version of my nnimap-split-fancy

(setq nnimap-split-fancy
      '(| 
       	("from" "stuff.*" "INBOX.stuff")
	("from" "no-reply@stuff" "INBOX.tmp")
	;; Invoke the BBDB
	(: (lambda ()
	     (car (bbdb/gnus-split-method))))
	;; Default mailbox
	"INBOX"))


The difference with Sebastian's fix from 24 Jul 2015 is that he uses
nnimap-split-methods nnmail-split-fancy, whereas in my case it is
nnimap-split-fancy.

In Emacs25, nnimap-split-methods is nil
In Emacs24, its value is nnimap-split-fancy

In Emacs25, when I reload Gnus, (r), nnimap-split-fancy gets the
intended value, and splitting works as before. So, somehow, m-x gnus
reads my .gnus file, and then forgets (some parts of) it.

Not sure what to do.. Not sure how to debug this either.

Would appreciate some pointers. Thanks