1. Simplification of path seems to be broken

2. At one time I managed to get tools "broken" by clicking on their

icons and getting all of them active in terms of the look of

respective buttons (down/up state).

Eww!!!!

That's actually down in some code that has a bit of an ugly state of things. That code needs to be changed and decoupled anyway, since that direct coupling is what is blocking switching to stock GTK+ toolbars for the vertical one.

3. If I draw a rectangle, then erase inside and start moving

rectangle, what I drew with Eraser will start moving away from

rectangle.

4. Erasing black rectangle is like looking for a black cat in a dark room :)

Oh! That needs some work. The eraser tool has its own style, so perhaps just picking a good style would work. I've not seen that myself since I changed it's style and that gets stored in prefs.

The choice might end up a little like the out-of-gamut warning color issue.