Tested here and still works fine creating unique filenames as needed; have you possibly disabled the option that tells SC to uniqueify filenames when there is a conflict?
I have not knowingly disabled it, and I did not see that flag when I looked in preferences.
I have switched back to 4.13 and it is working fine.
So, I reinstalled 4.15.0 to check the flag... but it is now working fine.
I was definately crook, now good... I don't know why but I will keep a close eye on it J.
Thanks for the quick response.