np duve, here is the link, 1 year old at least:
http://crawl.chaosforge.org/index.php?title=VaultThe term vault refers to any dungeon feature that is not part of the dungeon's normal layout. Vaults generally have a fixed layout, though many include random items or monsters, and some (notably Xom's altar vault) randomize the terrain as well.
This document solves any doubts,
http://crawl.chaosforge.org/Example_Vaults, check "Special Room:
"Special Room"
A re-occuring rectangular room without doors which contains a group of monsters with a theme:
Kobold lair (D:7-14, Orc:1-3): kobolds and big kobolds.
[...]
The user Tower did a very usefull job by creating an indeep article about Special Room vault (
http://crawl.chaosforge.org/Special_room) where a description table shows probability for each allowerd monster to spawn there as per dungeon level.
So we can assume luck always gets the last word, content creators though can make it less crazy than many would expect ("its all random", "get used to it", "human brain works like this").
Note: since articles are old they do not include any review made to the related code, which was rewised at least once since the good update about runed doors to prevent crazy OODs was more recent. So u may randomly blink when hiccough. Beware don't engorge too often!