Several issues exist with the IsSpread checkbox

[DrWhoCares]

Essentially. you should never manually change this flag.
You should have it automatically set via proper file naming conventions (see the README file), and avoid editing it manually.
I think it technically works manually, so long as you're making it for the first time, and you don't uncheck it after checking it the first time.

I have to redesign how it works at a later point.