No Raistlin,if you complete a queue and shift while the gauge is empty and then shift back it will be already full.The cases in which it is not full are just a few.
You can try for example shifting to a paradigm with only one job variation(the fastest) and see for yourself.

It canīt be explained by just saying the gauge fills while you shift.Itīs too fast.

Double shifting means shifting from paradigm A to paradigm B and then back to A.

I hope there is an explanation why itīs not allways full.