After various attempts to figure out what I might be doing wrong, I just confirmed the following behavior…
Edit a topic title using the forum toolset from forum view and the permalink for that topic gets appended so a /title-like-this becomes /title-like-this-1 … Attempting to strip the number from the slug results in yet another /title-like-this-1-1
This causes trouble when the forum has already been linked to since the original slug gets vaporized… 
Version: 5.0.5 Build: 8289
Jim, can you give me a few more details? just tried it on several here with no issue…
when you edit the topic title, are you changing the topic slug or not?
I can replicate this. I will open a ticket to get it fixed up.
Thanks Jim. You should be able to go back into the edit topic title popup and remove the offending -1 (or -1-1) and re-save and it should be OK. Be grateful if you could confirm that if you try it.
Guess I never subscribed to this topic, sorry for the late reply.
I’m happy to see this marked as fixed in 5.1! But for the record, when I attempted to edit the slug by removing the -1 it would then get appended as -1-1 and so on…
Thanks for the fix!