I have found a small bug related to the new tabbed editor component.
1) Create several query editor tabs with Ctrl-T;
2) In the first tab, type in and start a query that takes long (at least several seconds) but can be stopped by clicking on the red "X"; An UPDATE query with two tables worked to me;
3) Change to another SQL editor tab (the query should still run!);
4) Now stop execution of the mentioned query by clicking on the red "X";
5) Change back to the 1st tab: YOU CANNOT EDIT THE QUERY ANYMORE (the editor is read-only).
It becomes only editable if you stop the query execution being in the same tab.
So you have to start and stop the query again without changing to another tab.