When I was using a 2 by 2 infinite water source to collect water, the water block I collected wouldn't always be replaced and would remain as air. This appeared to be a block update glitch as taking water from any of the other 3 water blocks resulted in all 4 water blocks being replenished as if the empty block was water all along. However, if you attempted to interact with the empty block, it would have the properties of air and you would be unable to collect any water from it.

Video evidence: Water.mp4

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