I'd bet for mirror issues. Mirrors are out of sync and yum does crazy 
things then. Remove mirros list and use baseurl instead.
    

I tried that, but it looks as if the master repo has a primary.xml.gz file
that is woefully incomplete compared to the actual directory contents.
I think the mirrors are in sync, but they are synced with trash (or were
last night when I was looking at it in detail :-).

  

https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=208778

I have added some info about the issue.

Tim