Alright, this is what (I think) I figured out.
In order to have the article saved as draft, we need to have the auto-save option. If you leave the article alone for a while, it will save itself without causing any errors. You can check if it was saved by looking at the bottom of the writing box, where you have Word Count on the left and Last Edited on the right. When you finish writing you will see it says “Saving Draft” and when it’s done it says Draft Saved At [date]. If the article is long or has many links and photos it might take a while until it saves it, but at least you don’t risk losing everything by trying to save it manually.
I hope this helps people, as I’ve seen this problem reported many times on the support forums.
P.S.: Sorry if I’m not expressing myself too clear, I’m not a native english speaker, I’m Romanian.