In evolver mode, the following actions reset the undo graph:

* Pressing the "To Best Autosave" button or using a keyboard shortcut for that action.
* Using the "Ctrl-1" to "Ctrl-3" key combinations.

This bug doesn't occur in solo mode.

Why this is a real problem:

By clearing the undo graph, the bug prevents one from using "Undo" after performing the above actions. This means that all progress made by trying an alternate configuration is lost.

Having to be careful about the potential damage (e.g. always do "shift-ctrl-1" before a "to-best" etc.) breaks one's concentration. The interface should not get in the way of gameplay: "to-best" should work the same in solo than in evolver mode...