Floors and ceilings moving silently
The engine places the origin of the sound of a lowering or rising sector at the center of that sector. When a sector spans a large area, the distance between the player and the point of origin of the sound can be sufficient for the player to hear no sound, despite being right next to the sector. Additionally, if a sector is split into sections, only the first section makes a sound when activated, while the other parts are silent. This effect may be exploited by level designers to produce some unusual effects and notoriously affects the 10 Sectors contest PWAD since in many levels designers split various sectors to produce floor raising or ceiling lowering effects in multiple parts of their levels using only a single sector. The oddity is also noticeable in Memento Mori II MAP07 which uses such a method for a door that "jams" at random positions.
When the sound code was changed in ZDoom to place the point of origin of the sound at the nearest point of the sector from the player, the change broke some levels which deliberately used this effect, notably in Suspended in Dusk. As a result, a compatibility flag and map option was added shortly afterwards to optionally restore the old behavior.