If we're talking basic platform pedals I actually did something similar a couple weeks ago. I'd just finished a '73 Nishiki Professional but didn't want to take the hour necessary to clean, polish, and install a set of toeclips (plus I was losing the light) so I took it for a ride with unadorned classic road pedals. The first time a foot came off it surprised me, but the second time surprised me even more because by then I was being pretty careful. Apparently without the self-imposed limitation that toeclips afford my feet will do whatever they please. So you're not alone and, since we're semi-local to each other, if you ever see anyone doing the QWOP on a freshly-built old roadbike that'll be me.