I'll check this again... What's the condition of the plugs, dispack and leads? LPG is more demanding on the HT system and it must be in top condition 
I actually think the problem is mixture related from your description but these things need to be checked properly 
I'm not sure what condition the dispac and leads are in, I have replaced the plugs in an attempt to improve things but it didn't make any difference. I used NGK BKR6E's (single electrode, v-groove) and gapped them to 0.8mm.
I also believe it's in the mixture tbh. When the engine is cold it runs rough on lpg and can stall on idle. I think it may be running lean as when the engine is fully up to temp. it runs better. One other characteristic i've just remembered is when the engine fan kicks in, if the engine is idling the revs drop significantly and it switches back to petrol. I think this must be down to the extra current being drawn? If i'm driving and the fan kicks in I don't notice it.
Tunnie, my loom plug does point down? Do you mean the ECU plug should point down?? :-?