Clicking "undo" repeatedly within short intervals will make the subcubes end up in invalid positions

[Crushy]

While user performed rotations and the initial scrambling will not cause any issues, undo is currently not doing any checking before starting a new rotation, which may cause several rotations to be executed simultaneously and lead to subcubes being in invalid positions.

Possible solutions

• Refactor system to allow simultaneous rotations
• Use a similar approach to the user rotations and block input until the last rotation has finished