The confusion mostly comes from not knowing I pressed some button to get that popup while I was typing. It happened as I was typing, and grayed the post button out like Twitter does when you hit the post limit.

This caused me to think it was somehow length related. Long pressing or condensing some of the buttons in the UI would probably help. I'm not used to having so many icons right above the buttons I'm using to type.

It makes more sense now that I understand that the action was tied to an icon press. It could help to move the buttons away from the keyboard as well, or just have a post options menu. This would also clean up the UI.

You can also see in the attached screenshot that the message isn't even visible on my device until I happen to scroll down. It just looks like I can't post the note for some reason.

Thanks!