This issue was introduced in 17w47a.
Build waterways
Power a certain area of the waterway with redstone
Place the hopper at the powered location
The water flow was not intercepted as expected
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This is very strange. Placing a hopper in a powered location doesn’t update adjacent flowing water, but in all other cases hopper placement seems to work as expected.
Can confirm for 18w19a
Hoppers don’t send block updates at all when placed (they do send shape updates (observer update))!
Very annoying bug for survival playstyle. Please do fix!