Copying files and numbering, how do they work?

I use my Mac for graphic design.

With that, I often make copies of my files as the client makes changes.

The way I do that is I pick up the file with the [Option] key (which gives me the little green + icon as I copy) and then let it go in the same folder.

BEFORE I updated the OS, I would start with a file named this:

File 1.ai

When I copied this file with the [Option] key, the files would look like this:

File 1.ai

File 2.ai

When I copied File 2 with the [Option] key, the files would look like this:

File 1.ai

File 2.ai

File 3.ai

The numbers would automatically count up.

NOW that I've upgraded; I'll start out with "File 1.ai", but when I [Option] copy, I get this:

File 1.ai

File 1 2.ai

If I try to [Option] copy "File 1 2.ai", I get this:

File 1.ai

File 1 2.ai

File 1 2 2.ai

And so on. It's annoying.

Is this a setting? How do I fix this?