Thanks for the reply.
I scoured the 'net for more info and it seems many Alfa drivers report the same problem (and I too experienced this on my previous 164).
It seems the culprit is often the 'sender unit' - reports suggest it is somewhat fragile. I do keep an eye on the dipstick, and the level was great before AND after the perceived drop in pressure.
As well as making the 3.0 quieter, smoother and cheaper to drive, LPG also keeps the engine oil as clean as when it first went in
Cheers!