As others have insinuated the fuel system is not the best. In fact it seems to have a mind of it's own sometimes.
The main problem I've had is with the high level shut-off valves on the main tanks. They either didn't operate quickly enough or didn't operate at all (I wasn't about to keep p1ssing fuel all over the apron to find out). They seemed to be worse when cold. That was on the 604 by the way and I've only completely filled the 605 once so far so no way of knowing yet what it's quirks are.
Rather than rely upon them to function automatically I begin filling the mains, when almost full open up the aux/tail and once fuel registers in those close the mains off. If the mains weren't quite full I briefly open them while the aux/tail is filling and manage to squeeze a little more in that way.
I've never had it happen to me but am told that if the fuel supply is interrupted at this stage you'll never be able to recommence fuelling of the aux/tail except possibly by powering down the system and trying again. Not seen this first hand though.