What version of cms are you using? Sounds like an old bug in early 7?
That's pretty up to date.
It's been reported before and "fixed" I think. Might be broken again then :)
Experienced the same problem and managed a workaround.
Create the link as:
Worked for me.
@Daniel Ovaska what number was that bug?
That workaround worked, thanks. As the root problem still remains, I wont mark your reply as answer.
I also encountered this issue when using a custom route, see here: http://world.episerver.com/forum/developer-forum/-Episerver-75-CMS/Thread-Container/2016/5/custom-route-bug/
When adding a link to a internal page in the external link input filed in tinymce, linkitemcollection or url property the query paramets get removed and the link parsed to the internal page.
Example link: http://mydomain.com/mypage/?test=hello%20world
How to I add a link to a internal page with query parameters?