[EvanAnderson]

Yes. This is arguably the most infuriating implementation of undo/redo that I've used in any application.

It's worse than an undo that just wipes-out the document. In that scenario I'd just not use the feature.

The behavior in Excel tricks you into using the feature by working as you'd expect in a single document scenario. Then you open a second document and end up trashing one or the other when you undo the wrong thing.

I don't know how anybody ever thought this implementation was the right answer. Ever.

[melagonster]

more interesting part is, when you find these are shared in powerpoint and word, too.

there is not warning about I modified another file, if I dare to work on multiple task, everything probably wreck.

[fomine3]

Devil's advocate: For Excel, it makes a bit sense to have app global undo because sometimes Excel books refer other opened books' data. For Word and PowerPoint, it's hard to advocate because I've never seen referring other docs.