Well, I'm not too sure if there's a thread for this already (and I'm not going to look through the hundreds of threads), but I do believe there is some kind of bug that lets the text go off the thread if there's a link that's too long. It'd be nice if it were to be fixed.
There is a thread about this, I'm not sure if a message ever got sent about that. I think it might have been fixed on desktop but not mobile, but you'll have to look at the thread to make sure. It's in the archives.