Duke3D: Bug with overlayed spinning sector in E3L6 of "The Gate"
(Note: It is possible that the map was originally exploiting a bug for this.)
In the attached map, you will find a large spinning sector, overlayed on top of a stationary one. Hitting the switch will open a teleporter entrance that connects the two areas. Open the automap. You will see both sectors, with the outline of the spinning sector being also visible. Entering the teleporter is supposed to send you to the teleporter entrance of the spinning sector. However, as of the most recent revisions, this is no longer guaranteed to happen.
Wait until the spinning sector has completed roughly 2 complete cycles, then the destination will no longer be in the spinning sector, but rather the static one. In older versions (e.g. r6775) the destination moves slightly with every cycle, eventually converging to the middle. It is possible that this destination now somehow ends up in the wrong overlaid sector.