The glitch is no more!

And the LPG fuel level indicator goes "bip bip bip" as the system switches to petrol as the LPG runs (near) empty.

This was achieved with a new software update made to the system control unit that finally solved the problem. One thing is left to check later, the fuel reserve, to little and the system will not switch to petrol when out of gas, to much and the Corolla will be running to the LPG station far to many times.

Driving home that day, the engine seemed more "smooth" than the usual for the past few months, as I was told by the man that made the update, that was natural since the new software not only had the correction for the fuel level problem, but also had some other minor corrections made.