**BUG**
Concise problem statement:
Undo button does not light up and is greyed out in SuperMenu > Edit after editing a schematic.
(Using EE V1.0 1/4/14)
Url:
https://easyeda.com/file_view_Basic-comparator-circuit_dRLFXR8qI.htm
Browser:Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:26.0) Gecko/20100101 Firefox/26.0