When changing the owner of a wiki, wiki owner security access rights are not updated

Steps to reproduce:

1. Login with Admin
2. Create 2 global users: U1 & U2
3. Create a new subwiki and in step 2 set U1 as the owner and U2 as a member
4. Use DW to install the UI
5. You'll get a merge conflict for XWiki.XWikiAllGroup: choose "Keep the current version"
6. Hover over Home and click "Wiki Index"
7. Click "edit" for the new subwiki
8. Click Edit
9. Change the subwiki's owner to U2
10. Login with U2
11. Hover over Wiki; you won't see the Administer Wiki link
12. Login with U1 (the previous owner); you'll have both Administrative rights and the right to delete the wiki

Basically the previous owner (U1) has more rights than the current one. I think U1 shouldn't have any administrative right once he's no longer the owner.