Binder Width too narrow when I start new session

I’ve probably done something to cause this behavior, but I can’t figure out what it is.

The Problem:

Every time I open Scrivener the Binder is about half the width I’d like it to be. So I adjust it.
The next time I start Scrivener, it’s back to the narrow Binder width, so I adjust it again.

I’m a little surprised at how much this is driving me nutty, but there it is.

Any help would be greatly appreciated.