Excel 2011 Mac undo paste failure .. not a macro issue

At least, I don't think it's a macro issue. It's just a regular Office 2011 Mac Excel file .. a dot xlsx file .. yet I'm getting the same inability to undo a paste that others have described as being caused by macros, etc. In fact, there aren't even any formulae .. it's all just text (I know, I know .. what's the point of using Excel if it's all just text?) If I copy & paste but realize I've pasted the wrong thing, an undo command will not undo the paste but, instead, whatever edit I had done just before the paste. Is there any way to undo a paste in Excel 2011 Mac? This is a ridiculous failure that makes using Excel very frustrating.

Excel for Mac is very buggy in my experience.

I even have some spreadsheets that I saved in Excel, that cannot be reopened in Excel, yet which open fine in Open Office and even Preview.

Yep .. Excel bytes it, big time. If I weren't collaborating with other who use Excel, I'd ditch it for sure.