To reproduce: 1. Open a plain text document in Safari. 2. Find some text that only occurs once on the page 3. Create a selection that overlaps the text you noted in step 2, but does not entirely encompass it 4. Command-F to bring up Find UI, and search for the text you noted in step 2 This should find the only instance of the text, but fails to do so. This works correctly in HTML.
It seems that PDFs would have this same bug, though I tested just now and could not reproduce the problem in a PDF. We should understand why.
PDFs don't have this same bug because we search the entire PDF in the wrap case; this is the same behavior as HTML.
Checked in fix.