Unintentionally Modifying Multiple Sheets Simultaneously in Same Workbook

I don't how I did it, whether it's a bug or a "feature", but when
working in a workbook today with multiple sheets, some of which are
copies (move or copy), I changed a row in one sheet and another sheet
had the same row changed also. My theory was that by choosing multiple
sheets so I could print "all active sheets" I must have left those
sheets active and hence the change was applied to both sheets. But
even deselecting so only one sheet was active had the same result.

Is this a bug? Am I losing my mind? This is making using Excel 2004
too exciting for me.

Any help is appreciated.