I didn't either until I lost my draft and it made me really tear up because I missed my daily post and the LOH contest.
So if it's by only clicking "save draft" that the "restore last draft" can work then what's the essence of having the "auto save draft" and "auto update preview" features?
If they are there then they should work as expected just like in other frontends. We are looking forward to having more users try posting through the UI then it's important that all features on the UI work as expected to minimize such cases. If it's unreliable then it's not the best. Except they don't work on mobile.