This bug allowed things that would otherwise spawn on the map edge, like traders, wild animals, and most dangerously ambush squads, to spawn in the middle of the map where the edge would be if it was square.
Goblins in your base...
Oh I had this happen once.
I had a long east-west oriented map once and the fort was likewise enlongated. The dining hall was partly built on the surface on the east end, just left of the center of the map.
M = mountain
V = volcano
F = forest
R = river (minor river 8 tiles wide IIRC)
X = center of map
MMFFFFFRF
MVMMXFMRR
MMFFFFMMR
Total embark tiles: 27
Only slightly higher than my norm of 25 in a 5x5 map.
Coal and flux were under the forest with deep silver and gold and the mountains had iron and deep galena.
The majority of the fort was built into and on the spur between the volcano and center of the map. Main access was over a bridge between that spur and the mountain near the river.
For eight years sieges (x7) and ambushes(like 100 of them) only appeared from the north and south sides of the map, so there were no problems.
*A vile force of darkness has arrived!*
"What the hell? They just spawned IN my dining hall."
90 goblins + 40 trolls. Most of the squads and a few of the trolls spawned in the dining hall.
170 civvies were in this room or the rooms on the 3z-levels below. The only entrance to those rooms was through the dining hall.
*order all military active and stationed at the entrance to dining hall*
*unpause*
Epic carnage of a scale beyond what you can possibly imagine ensued.
In the end I had lost 192 of 260 dwarves (167 civvies, 25 military), had 30 dwarves severely injured and all my doctors were dead and the remaining 38 functional dwarves immediately imploded in a tantrum spiral and vast clouds of FPS-killing miasma. Also, a troll smashed a magma forge and a bunch of fire imps got into my wood and food stockpiles with predictable results.
It was totally worth it. I'd do it again in an instant.