Underlined text could not be searched in a sentence in Editor, with Find/Replace

Steps to reproduce

1. Install a new Confluence 6.9.1
2. Create a page with some text underlined
3. Try to search those word with Find/Replace

Expected Results

All the text should be able to search

Actual Results

Notes

Noticed that, If I search the word modified, It can be found with the Find/Replace.
But If I search with the whole sentence, It does not return anything:

More test: