Steps to reproduce:
 
1. Start stock emacs 25.1:
$ emacs -Q test.org
 
2. Write a headline
* Test
 
3. Issue C-c C-c and the headline to add a tag
* Test           :test:
 
4. Modify the headline to include a link.
* Test [[http://test][test]]          :test:
 
5. Everything appears to be rendered correctly, but when viewing the source, it really looks like:
[[http://test][te]]st

6. To make it render wrong and become very obvious, change the link description to have multiple words.