You can expect data to be destroyed when automatically parsing csv/tsv (default behaviour), especially because it's dependent on the last settings used in the text-to-columns wizard.

Then there's all well-known bugs like floating point addition and locale-dependent function names and 1904 dates.

Conditional formatting accidentally pasting is all over the place.

As others have mentioned, copying and pasting in Excel is bizarre. Highlight the cells to copy; select copy - the source cells now have marching ants around them; perform any action that causes the marching ants to disappear and that content can no longer be pasted. It’s as if those cells are locked as the copy buffer as opposed to some in memory copy like every other copy operation.