(1) Open a web page in a web browser (HTML)
(2) Open a new spreadsheet document in Calc
(3) Copy some content from the web including one or more graphics
(4) Paste the content to the spreadsheet
(5) Select undo from the edit menu
The result should be a blank spreadsheet. Instead the grafics are still in the
spreadsheet.

This can be very annoying, because web pages often contain a big number of
little images. Copying accidentally from the wrong source or to the wrong
destination can screw up your whole spreadsheet, since you cannot go back the
last step you did. But that is exactly, for what the undo-function is ment.