When using the Afterburner theme with Moodle 2.6+ (Build: 20131122) I am unable to use the "add an activity or resource" dialog since it is greyed-out and does not provide any functionality.

This only happens on courses which are already populated with material. The dialog comes up alright on empty courses.

I could reproduce this phenomenon on three different Moodle installations all running the same version of Moodle, though.

The problem can be circumvented by using a different theme. However, I would appreciate having this problem fixed for Afterburner, sicne that is what have been using.