incomplete packet of petroleum in a pipe after a shutoff

To fill the fuel tanks of my rocket, I've installed a long pipe that can contain the 900 kg needed for 1 tank.

It's controlled by a liquid shutoff at each side.

But sometimes, the last packet of fuel refuse to be filled at 10 kg.

On this screen, as you can see, the liquid shutoff is activated by the aytomation grid. There's 10 kg of petroleum at its input. But the packet in the ouput pipe stays at 1666 g.

But it not happens every time.

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