Sadly, it appears that this will never be fixed. I recently upgraded to Version 14 and just ran into the problem (again). Checking the forums, I still see my original post from 13 years ago ( Debug session 'stuck' on ORA-03114 - not connected to oracle loop ).

The problem can occur when a debugging session is left 'executing' too long, and Oracle times out the session. So, the previous workarounds (like killing the Oracle session) won't work, because Oracle has already killed the session on the database side.

I would have thought it should be a pretty 'simple' fix in PL/SQL Developer - when the user tries to close the window and receives the "Test Window cannot be closed, Script is still executing", and then clicks the Terminate button, and gets the error:
Error during debug step:
ORA-03114: not connected to ORACLE
Debug session terminated.

clear the 'flag' that indicates that the session is still executing. Since the session is already disconnected from Oracle, there is no need to be concerned about a dangling process on the Oracle side.

The only way I can see that will get out of the situation is to kill the PL/SQL Developer app in Task Manager. That is a bit drastic, but since there is no known work-around, that is the only way to solve the issue. (Trying to close the window from the Task Bar (or by clicking the X in the upper right of the application) just pops up the same "Test Window cannot be closed, Script is still executing" dialog.)

This problem should be very simple to reproduce - start a Debug session, disconnect the PC from the network, and try to do a step. Once the connection times out, the error should occur.

I'm assuming that fixing this is too low on the list of bug fixes for AA, likely because an insufficient number of people have let AA know that they have this problem. So if you do have this problem, let AA know, so it might inch up a tad on their 'bugs to fix' list.

Thanks
Juan