This appears to be the actual thread title:
<asp:EntityDataSource not working in VS2015 Visual Web Part
However, it's output in the thread list as:
<asp:entitydatasource a="" web part<="" visual="" vs2015="" in="" working="" not=""></asp:entitydatasource>
So it's not that the forum is stripping anything out. It seems like it actually added a closing bracket and the ending tag where there were none originally (as well as munging the text into the element), and that's what prevented the thread title from rendering.