once i tried to bunny hop with platform pedals - kinda forgot i wasn't clipped in - hurt quite a bit when i thankfully landed on the seat. (as opposed to the top tube or crashing)
Whew, very lucky you planted yer butt on the saddle. My more frequent problem is pulling the rear end too high when I'm clipped in, since I bunny hop on platforms just as often as when clipped in.
Just yesterday I encountered a problem that may be common for folks that go from clipless to platform: I struck pavement while pedalling through a turn. If I'd had SPDs on that probably wouldn't have happened.
Luckily I've never gone down from a pedal strike on the street - knock on wood.