Operations to avoid with multiple sheets?

Operations to avoid with multiple sheets?

Are there any operations which should be avoided when working with multiple sheets?

Twice now, I've had something more or less like the following happen:
 * Do some work on sheet A
 * Switch to sheet B and work there for a little while
 * Switch back to sheet A to find it altered in strange ways (missing or quasi-missing rows?)

It's kind of disconcerting. I want to make sure it's not something I'm doing wrong before reporting it as a bug, though.

[The work on Sheet B has involved column resizing/adding/deletion, data changes, formatting (changing font), and copy-paste using the keyboard shortcuts.]

Thanks for any help!

[Apologies if this gets posted twice; I tried submitting it through "Feedback" and clicked the "Post to Forums" checkbox, but it doesn't seem to be showing up.]