Link is incorrectly added to the end of the page when the first word on the page is highlighted in wiki markup

To reproduce:

1. Add/edit using wiki markup, with multiple lines of text
2. Highlight the first word on the page
3. Click Insert/Edit link, and search for a page to link to
4. Click OK
5. The link is added at the end of the page, instead of replacing the highlighted text.

This is related to CONF-12302, but it happens on all browsers, and only with the first word on the page.