A reader asks:

"The checkbox for Tools>Options>Spelling>Ignore original message text in replies & forwards has a checkmark in it. On the Mail format tab, there are no checkmarks in the two MS Word 2003 checkboxes and HTML is set as the editor.

Regardless of these factors, spell check still runs on original message text in replies and forwards sent to us in Plain Text format."

Are you using the option to "Prefix each line with"? This will cause the problem you're seeing. Normally there is a warning when you set a prefix, but it doesn't display under certain conditions.

Look for this option in Tools, Options, email options, On replies and forwards section.