Duke3D: Player cannot enter sectors that have a height of 6144 if they are not aligned with the floor or the ceiling of the adjacent sector
Another issue that began with the clipping changes of r7428 (commit d060ca95), the most recent commit that attempted to solve this problem was r8640 (commit 744a46f1). This did solve the problem for all but a single vent in DUKEDC3.map. Unfortunately this vent happens to be one that leads to the yellow key.
From what I can tell, entry is prevented for any sector that has height of 6144 (1024 * 6) and which does not share a ceiling height or floor height with the adjacent sector. Sectors of this height that do share at least one of the two can be entered by player, albeit with some effort. The attached map showcases this behavior:
Also note that sectors of size 7168 (1024 * 7) can always be entered, and sectors of size 5120 (1024*5) can never be entered, even prior to r7428. Since multiples of 1024 are common for sector heights, I believe that there may be usermaps out there that cannot be completed because of this.
Another related, but minor issue is that areas of size 6144 have the player move at crouching speed, whereas previous to r7428, this speed was the same as if the player were standing upright. I haven't encountered any maps where this would become an issue, but I think it's worth pointing this difference out.