Thanks for your feedback. I will try to have a look at this tomorrow and see what the problem is. Hopefully will be able to fix it and provide an update by next week.
I took a look at the widget and I can't seem to see any major issues. The only thing i notice is if you press on the image button without having the cursor in the text area the button won't do anything. If you click into the text area first and press the image button it seems to work.
I seem to be able to replicate the problem, but just need to find how to solve it. Seems a bit odd though, because it works fine in the default theme but seems to have an issue in the cerulean theme.