Minecarts change behaviour and suck items from hoppers depending on the direction the minecart is travelling.
Minecarts travelling North and East only suck items from hoppers when the hopper is facing the track. This is expected behaviour.
Minecarts travelling South suck items from hoppers facing North or South.
Minecarts travelling West suck items from hoppers facing East or West.
This is unexpected behaviour, minecarts should only suck items from hoppers facing the track.
Steps to reproduce:
Lay track north south.
Place hopper alongside the track facing either north or south (NOT facing the track).
Place items in the hopper.
Minecart with chest travelling north will NOT collect items from the hopper (expected behaviour)
Minecart with chest travelling south WILL collect items from the hopper (unexpected behaviour)
Reproducible in east/west direction too.