Delete right shown in the UI when delete right is not present but undelete right is present

To reproduce:

• create a page
• go to the edit -> access rights UI
• explicitely give delete right to a group or user
• go in the object editor, you'll see the XWikiRights object with allow and the "delete" right selected
• change the selection to give the "undelete" right and only this right (no delete right) and save
• open access rights editor again, delete right will still appear as checked.

Optionally, you can actually try to delete the page with a user from this group (or the user itself if the right was for a user) to see that it cannot actually delete it. Make sure however that it's not the author of the page, since author always has the right to delete.