Group nnselect:... contains no messages

Hi,

gnus-group-read-ephemeral-search-group does not seem to work.

I’m using HEAD from the master branch and this config:

(setq gnus-select-method
  '(nnml "Email" (gnus-search-engine gnus-search-notmuch
                   (config-file "/home/peter/.notmuch-config"))))

When doing a search on the command line, I get:

notmuch search --output=files --duplicate=1 "identit*" | wc -l
-> 617

notmuch search --output=files --duplicate=1 "identit*" | grep Mail/tmp | wc -l
-> 1

So there is one message in the group tmp that matches the query.

But (with gnus-verbose = 8):

Doing notmuch query on (tmp)...
Search engine returned 619 results
Gnus search returning 0 results
Group nnselect:nnselect-87o6xfr8pd.fsf contains no messages

Could you help me please to get a working search?

TIA for any hints,
-- 
           Peter