Internal links with duplicate query parameters are merged

Description

Steps to reproduce

1. Create a page with an XHTML property.
2. In the TinyMCE editor, create a link to a page and enter "?arg=1&arg=2" into the Remaining URL field.
3. In the Create link dialog, press OK.
4. Publish the block/page.
5. View it on the site.

Expected:
The page renders with a link xxx?arg=1&arg=2.

Actual:
The page renders with a link xxx?arg=1,2.