When exporting to a file with a name ending in a full stop, Photoshop creates two files...

When using Quick Export (I have not tested other export engines), when saving a file with a name that ends in a full stop, thus resulting in two dots in a row before the file extension, Photoshop saves out one empty file with the proper name, and one file replacing the first of the two dots with an underscore (_) with the actual file content.

For instance, exporting "full stop..png" will result in:
full stop..png (0 bytes)
full stop_.png (actually containing what the above SHOULD contain)

Note: Before someone comes in with apologetics telling me that Adobe can do no wrong and never has bugs and that a file should not end with "..png" etc, just don't. That's incorrect, as evidenced by the fact that it DOES in fact make a file with that name, but writes to the wrong file. (Also as evidenced by the fact that it's just not an invalid filename and so don't make things up, K.)

This is a bug and needs to be fixed.