Re: Got it, at last!
the effect is very fragile. If you try the same on a file saved as .nwctxt the keys '+' and '-' work as expected!
That is because your attachment is a corrupted file. Saving it to a text format removes the corruption.
It may be that the file got mangled on your storage device, by Windows, or by another app.
It is possible that NoteWorthy did not cause the bug.