Solver is fast, and when is not, you know that and it is provided a way to fix it. Anyway there was remaining still for slow video cards a component that was still slow, on many notes: the tree view.
As a fully new implementation is hard to be done, and knowing why may be slow: mostly that we rebuild the tree every time and it's icons displaying take some time, for complex shapes, I've did optimized the common case: when you add a new shape is added to tree.
Also the timing of building a tree is also taken in account and if is over a threshold it will propose for user to disable it.
So with this change the adding things in scene will be "smarter" and faster and will make you to work with bigger scenes and with less pauses.