Get blood extractor with at least 1000mb.
Put extractor into auto-supply mode.
Pick up a stack (16) of empty buckets into your hotbar.

Expected:
Player now has 16 filled buckets of blood
-OR-
Player has 1 filled bucket of blood and a stack of 15 empty buckets.

Actual:
Stack of buckets transforms into a single bucket of blood.

EvilCraft-1.12.2-0.10.48.jar
CyclopsCore-1.12.2-0.11.4.jar
Minecraft 1.12.2
Forge 1.12.2-14.23.1.2603
Found on dedicated server. Confirmed in single player.