URLs with query strings break target="_blank" in custom menus

Setting the target in custom menus doesn't work if there is a query string appended to the URL.

Setting the target works fine with menu items like this:

Web Site | http://www.website.org" target="_blank | This is a web site

But fails for menu items like this:

Web Site2 | http://www.website2.org/?page_id=66" target="_blank | This is another web site

In the HTML for the page, the link for website2.org shows up like this:

<a href="http://www.website2.org/?page_id=66%22%20target%3D%22_blank">Web Site 2 </a>

I have checked this on multiple themes and it always happens. I also thought it might be a filter but the only filters I have enabled are: MathJax, Activity names auto-linking, Multimedia plugins, and Display emoticons as images. None of these seemed likely to mess with URLs in the menus.