Resolution: Works As Intended
Minecraft 14w31a, Minecraft 1.8, Minecraft 15w40b, Minecraft 15w46a, Minecraft 16w33a, Minecraft 1.11, Minecraft 1.11.2, Minecraft 17w06a, Minecraft 1.12 Pre-Release 6, Minecraft 1.12.2, Minecraft 18w05a, Minecraft 1.13, Minecraft 18w31a, Minecraft 1.13.1, 1.15.2, 20w22a, 1.16.3, 1.17.1
MinecartHoppers completely ignore the TransferCooldown tag.
The variable field_174900_c (BlockPos) is only set in the constructor but after that never changed:
BlockPos.ORIGIN is new BlockPos(0, 0, 0). So when it later tests if the current BlockPos of the minecart is equal to the stored block pos it will fail (unless it is at 0, 0, 0).
So is sets the TransferCooldown to 0 and after that tests if it can transfer, so the test will always (unless it is at 0, 0, 0) succeed, causing it to pick up items with a speed of 1 item per tick.
The reason why the BlockPos is tested might be because the TransferCooldown is initialized with -1, but as the canTransfer() (rather cannotTransfer()) method would then return false it would work anyways.
Testing for getBlocked() seems to be not needed as onUpdate() seems to be called only when the MinecartHopper is not blocked.
The wrong names can be caused by MCP as isRemote() is described as
"This is set to true for client worlds, and false for server worlds."
which would mean that hopper minecarts would not work in client worlds.
The method getBlocked() is described like this:
"Get whether this hopper minecart is being blocked by an activator rail."
Which makes no sense as well as then a blocked MinecartHopper would collect items.
I hope it is alright, that I added that much code from Minecraft here