Duke3D: Opening the newgame menu clears the E1L8 (usermap) slot
As reported on the forums, as soon as one confirms the "Abort this game?" dialog and enters the newgame menu, the E1L8 slot is cleared, causing any restarts on death in a usermap to revert to the default E1L8.map.
In fact, this occurs as soon as
m_volume_number != 0 or
m_level_number != 7.
From what I can tell, this has been the case for over a decade worth of revisions, so I'm going to assume this has always been the case.