There's a bit missing - the regulations [Drafted after McLaren stopped on track in Canada '10] also say you have to make it back to the pits, and are only allowed to stop if there is a "force majoure", thus the combination of both logically requires that you have at least 4l of fuel left to do your inlap and take a fuel sample. As the fault was human error, and could have been fixed when they knew about it, it's not considered "force majoure" - the bit that is surprising to me is that it applies across the board, I would have assumed that each session stands alone, and would have expected Q3 times to be deleted...

On your other comments - you cant use 2 fuels, they get scrutineered at any time, not just the end of Q3. Interestingly the fuels also have to be within +- 12 degrees C of ambient too, to prevent supercool fuels being used, also, the fuels are supposed to be normal road car fuels, although it's pretty clear that they have at least some enhancement above what goes in the pumps on the forecourts - I'm not sure how they regulate what is considered a deviation....