Setup Factory installer leaves behind folder which cannot be deleted...

I have a working installer created with Setup Factory.

After EVERY run (which I'm doing a lot of during testing), the setup completes, but always leaves a folder behind in:

C:\Users\<MyUserID>\AppData\Local\Temp

The folder name left behind will be

_ir_sf_temp_<incrementing counter>

The only file left in the folder is a TFT file, which seems to be the font which is used for the background window (I know this as I have changed fonts there, and it changes the file left behind).

I cannot delete this file manually from Windows Explorer.

Can anyone shed any light on why this is happening, and how to get around it?

Thank you in advance...

Cheers
Robert