> But it is only liquid because it is under pressure. As soon as some
> liquid is in the lighter it vaporises to fill the chamber and if the
> resultant pressure is less than the pressure in the gas cylinder more
> liquid will go into the lighter until the system will reach stability.
>
>> Yes, adding liquid to the lighter gives back a bit of pressure for the
>> lighter's side, but not enough. The fresh liquid could vaporize to
>> provide more gas but that transformation requires a lot of heat which is
>> not available at the refill time.
>>
> The heat is taken from the air and the hand that is holding it. You can
> feel the lighter getting cold and you can hear the butane rushing into
> the lighter. The sound will stop when the pressure has equalised and the
> lighter will continue to fill up.

I haven't had chance to think in detail what is happening (nor do I have 
much experience with refilling lighters), but I suspect a good 
understanding of vapour pressure and how it changes with temperature is 
required:

http://en.wikipedia.org/wiki/Vapor_pressure
http://en.wikipedia.org/wiki/Butane_(data_page)#Vapor_pressure_of_liquid

Also bear in mind that it might not be 100% pure butane in the refill 
(or there might be some air in the lighter), so you better also know 
about partial pressure :-)

http://en.wikipedia.org/wiki/Partial_pressure

It sounds to me from what you describe that it's got something to do 
with things heating up or cooling down, causing the vapour pressure to 
change. An interesting experiment would be to prepare the lighter to be 
cooler or warmer than the refill canister and note any difference in 
behaviour when it is refilled.

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