Arduino IDE 1.6.7 undo function screws up the whole code, and even causes exceptions

The undo function in the Arduino (Genuino) IDE often works wrong and screws up the whole code. You can try it yourself by typing some lines, doing some changes at various locations and then using the undo function. It often fails and deletes/adds wrong text.
I'm using W7ProX64 SP1 and Arduino (Genuino) IDE 1.6.7

Start by reproducing the undo failure in Arduino IDE 1.6.7 on Windows 7, using edits at several locations as described. Trace the undo behavior and any resulting exceptions; done means undo restores the intended text reliably without corrupting the sketch or throwing exceptions.

Written by the indexing model from the issue text.