It sounds like your lying the gas cylinder on the side, to begin with there is enough heat in the stove feed pipe to vapourise the liquid gas that is leaking into it from the cylinder, as the vapourisation of the gas cools the pipe it freezes. it remains as liquid and reaches the nossle resulting in large flames, probably orange,and maybe extinguishing the stove due to a blockage or a little explosion. The half full cannister didnt leak gas ?
Try anglin the cannister (more) a bit like this, this i think fits thoes cannisters
http://www.amazon.co.uk/Coleman-205168-Powerpack-Single-Burner/dp/B0030BGA5U
Propane is very powerful, it can be a bit much for butane stoves.
Thanks very much for your thoughts, I'll try angling the bottle and see. I didnt get chance to try it out again today but it barely got above freezing all day so perhaps not the best day to try tests.
I'll post back when I've had chance to try it some more
Atb
Bob