It wasn't odd at all.
Such lengths as 55 or 58mm gave perfect lifesize viewing with viewfinders of the SLRs they were introduced along with.
That is one of the reasons.
Another might be that it is easier to design a superfast lens with narrower field of view and longer clearing distance from the swinging mirror, thus many of the early super-fast lenses (f/1.2, f/1.4) were slightly longer.
Frantisek
I think Pentax had the first 50mm 1.2 lens as all 1.2 lenses until then were 55mm or 58mm.
Andre
