Daikatana PlaneFaces off by one

[snake-biscuits]

looking up Face.plane in Daikatana maps to confirm the reverse lookup

>>> x = {k: {f.plane for f in [bsp.FACES[i] for i in vs]} for k, vs in bsp.plane_faces().items()}
>>> {k - list(v)[0] for k, v in x.items()}
{0, 1}

Sometimes Face.plane is 1 less than bsp.plane_faces says it should be,
All the indexed faces are off tho, by the same amount

>>> bsp = bsp_tool.load_bsp("E:/Mod/Daikatana/pak2/maps/e1m1a.bsp")
>>> {f.plane for f in [bsp.FACES[i] for i in bsp.plane_faces()[5]]}
{4}
>>> 4 == 5
False

Using List[List[int]]:

>>> len(bsp.PLANES), len(bsp.plane_faces())
(8194, 8194)

[snake-biscuits]

Might be related to how the Quake engine stored 2x each plane?
Odd / Even pairs grouping inverted copies