I'm running the Beta 3 version of WP 3.6 and a few of the tool icons are not showing in the editor. They were working up until the Beta 3 release, which also changed the font/look of the tool icons in the text editor tool bars. They are there, just not displayed. And they still work when clicked. When I hover over their spot, I see an empty box and a pop up that tells me what they are. The affected tool icons that I am using are:
Also, the font background color sort of displays, but only as an underline.
This is the best plugin ever and I recommend it to every client and won't install a site without it. I'm sure you have your hands full with changes to 3.6 and appreciate all of your hard work to make this plugin available.