First, I would make the invisible characters visible (Ctrl+Alt+8) and see if anything wierd is showing. I would also check the Draft view (ALT+V,D) to see if anything shows up there.

Try stripping all formatting from the paragraph(s). Select all the relevant text, then press Ctrl+Spacebar, then Ctrl+Q. With the text still selected, open your font formatting dialogue and see make sure that all the checkboxes for Hidden text, etc. are completely clear.

Does this solve your problem?