Dropping into gear

Faulty spring not resisting weight of lever. Cheap easy fix.  My spring de-laminated and when removed fell into 2 halves in my hand.

I suspect that, given the difficulty you are having selecting neutral, and as it has only happened once, on that occasion I doubt neutral was fully engaged. I have experienced similar on more modern, as well as older machines; think Italian.... I got, and remain, in the habit of never just dropping the clutch lever once stationary and (hopefully) in neutral, but feed the lever out gently, whilst holding the front brake on.. On more than one occasion it has wanted to creep forward.....