Group subscribe tab-completion

[xyblor]

When I want to subscribe to a newsgroup with "U", tab-completion does
not work, unless I have read the active file with "A A" or
"b". Otherwise, the only valid completions are the groups I have
already subscribed to.

The Gnus tutorial led me to believe that tab-completion should always
work, so I wonder if something's wrong. Shouldn't the newsrc.eld file
save a list of all the available newsgroups, so I don't have to read
the whole active file every time? I suspect this isn't happening
since it is very small (4 KB).

Thanks for any advice.