I noticed that when I had a few new (unsaved) editor tabs open (with code in them) and I closed SQL Developer without saving (deselecting the unsaved tabs), next time I opened SQL Developer, the start tab would be open by default and the previously unsaved tabs (at least a few of them) from the previous session would be still there, but would disappear as soon as I clicked on them.
To reproduce this, I opened SQL Developer and opened one new tab from one of my database connections. I made a query, ran it and then closed the application without saving the query (tab). When I started SQL Developer again, the unsaved tab from the previous session was not there.
So I opened four new tabs from two different database connections (two tabs from each database), ran a query in each of the tabs and closed the application without saving the queries. When I started SQL Developer again, two of the four unsaved tabs from the previous session were still there, both from the same database. As I clicked on them, one by one they disappeared.
If they were closed without saving them, they shouldn't appear again when SQL Developer is restarted, so this is a bug, isn't?
It is indeed a bug and we're looking into it.