I see that there is a thread already here for the same issue: http://www.sitefinity.com/developer-network/forums/general-discussions-/radeditor-in-sitefinity-10-1-6500-x-removes-mailto-links-upon-save, but there wasn't any traction there and I think this is the right place to report this.
In Sitefinity, 10.1.65xx.x (including 10.1.6523.0), the RADEditor removes mailto: links from a dynamic content when you save it. Here are the steps to reproduce the issue:
Normal links work perfectly fine. And this happens in all dynamic content types like News, Blog, etc. The Content Block widgets don't have this issue.
What is going on here? Can someone please clarify? This is causing a serious block in our Sitefinity development.