The awesome Eric Lamb helped me track down the fix for this problem. It isn't related to the CP URL change. It's a problem in the addon file.
Change line 326 from:
$out = '// THIS IS TEST';
$out = '';
I was able to fix the plugin by updating the ext.mx_title_control.php file on line 333 and 338. I replaced the following code:
I see from your MX Title Control GitHub Issue that you've fixed your issue. Nice job mate!
For any other readers the solution, which is a patch Joe submitted is listed here : https://github.com/joeczucha/mx-title-control/commit/9b0851146e3edc55442879affd3a6e4e9ff3df63
This thread is a few months old, but the solutions provided so far have not worked for me. Until MX Title Control is updated for 2.8.1 (it still isn't as of posting), a simple fix to modify the "Title" and "URL Title" labels is to simply add some JS within the "instructions" field of any field within that channel's field group:
<script>// We're using ...
You might try applying the patch posted on this Bug Tracker: https://support.ellislab.com/bugs/detail/20165