Testopia: Unable to save edited Category (from Categories tab) in Testopia for a particular Bugzilla product (Testopia-Bugzilla integrated))

When editing an already created Category (from Categories tab) in testopia, a small red arrow shows on the top left of the 'Name' and/or 'Description' column text boxes. It shows an update and a cancel button, but clicking on update doesn't save any changes and the red arrow still shows.

Naturally, the changes are discarded as soon as it is refreshed.

Working on Linux Fedora 23 with Bugzilla 4.4.12 and Testopia 2.5 and I have tried disabling any access control issues (temporarily for debugging only like SELinux) but received no success.