When renaming a tag, the same tags but with different case are removed from other documents

Steps to reproduce (tested on versions XWiki Jetty HSQLDB 15.10.11 and 14.10.21)

• add a tag (e.g Test) on a page (e.g Page1 )
• add a second tag with the same name but having different case (e.g TEST) on a distinct page (e.g Page2)
• when clicking on any of the tags both pages are referenced as being tagged (e.g for both  Test and TEST the pages listed as tagged are Page 1 and Page 2)
• rename one of the tags to use the same name as the other with different case (e.g rename TEST to Test)

Expected result:

• all pages (previously tagged with one of those 2 tags with same name and different case) should still be the tagged (e.g Test tag to which we renamed TEST tag should be shown both on Page1 and Page2)

Actual result:

• the tag with the name used for the rename action gets deleted from the previously tagged pages (e.g on the previously tagged page Page1 the tag Test was deleted and only Page 2 is tagged with Test tag)