I’ve just tested it myself, and it goes as follows:

When you post within your current 360 second cooldown period of time, you will see a message such as this one (I used your images here, but on another platform as imgur images are not shown on Bitcointalk):


If you then return to the prior screen and post the content again, you’ll see the subsequent message:


In other words, the system should probably display the first message each time, but once you attempt to post a given content, and retry again, it shows the second message without actually posting the content on the forum. It does save it to the Drafts, which could explain why the system "believes" that you’ve already posted the content (albeit to the Drafts).

It’s something that is not aligned really with what the proper workflow of visualized messages should be, since you really haven’t succeeded in posting the content on a thread. I doubt that it’s going to be changed though.

Bear in mind that, when your Activity reaches 15 (or higher), posting cooldown time becomes much lower, as per the formula shown on the second post on this thread (75 seconds tops), and decreases as Activity increases.