Oh hey, cool, someone's actually using my installer.

As for what you're talking about, yes, I have noticed those issues as well.
I should probably note that this install is experimental. It doesn't crash, but the interface is not entirely usable either. Also, there is currently no tablet pressure support. (Or any tablet recognition whatsoever.)

To begin with, pretty much every icon on the bar is useless. This is how gtk quartz currently handles pop-up windows. I'm told that this issue will be fixed in the next version. (I will then repackage MyPaint with the new gtk version.) If you open one dialog up on accident, you can close it via "esc".

If you wish to modify your brush settings, for the time being, please use the "Brush List Editor", or "shift B". If you want to hide the entire toolbar (due to it being nigh useless, and the fact that it's new), simply chose "View - Toolbars - Menu Bar Only". Not a very nice solution, but it's the only one that works.

What package are you using? How did you install MyPaint? Do you use X11?