One thing I've noticed in SS, WE, and SS Pro, is that very often the undo button does not undo the previous action, or at least not as I would expect it to. I have been unable to determine exactly what this tool uses to determine the previous action.

The help file has the best explanation that I have seen -- discussion here.

Thank you Bruceee. I have to agree with the person starting that string though. It seems buggy to me. Undo is undo, so I'm not sure why an explanation would be necessary in the first place. I would love to see SS simply undo the last action without all the if's and's or but's. Sometimes trying to undo my mistake gets me into more trouble than the mistake. I guess I need to learn not to make all those mistakes. (hee hee)