Near-duplicate created during skip all operation

When I ran two identical folders against each other to create checksums, I clicked skip all like usual. But, for whatever reason, teracopy created an additional copy of a file that already existed in both the target and source folder. And, weirder still, is the fact that it botched the filename, so instead of "filetitle.jpg" for example, teracopy created "filetitlejpg" in one run-on.

You see that? It's not a proper extension, so it wouldn't open.

Now, that's nothing I can't fix by adding the decimal myself to create the .jpg extension, but...why? Why would teracopy not only copy something I already have (in both folders, no less), but screw it up too?

Now this has me wondering how many copy operations teracopy might've botched in the past that I just never noticed (filenames don't affect checksums, after all). Has anyone ever experienced a glitch like this? How seriously should I take this? Are there failsafes against worse screwups? Because if not, it kinda defeats the purpose of a program like this.