Fix crashes when changing Mouse operation

[hugtalbot]

Fixes #268

[epernod]

Need to check:
OpenMouse operation -> change to spring operation -> change value -> close menu -> reopen -> check value has not been reset

[th-skam]

Need to check: OpenMouse operation -> change to spring operation -> change value -> close menu -> reopen -> check value has not been reset

If that's what was needed to check, I can verify that doing the above does not reset the value.