Jetpack "Custom Message" error

I’ve noticed sometimes Jetpack’s “Custom Message” when publicizing things auto-fills with text.

In the last of my last post, left an old title of a post which I changed. So the wrong title went out, and there’s no way to fix that once it’s publicized.

Is there a way to make sure the Custom Message field is *never* populated unless I actually type something in. Alternately, I’d take turning it off forever rather than having the wrong text go out on my posts.