just tried out the newest builds of Core and Inventories, but I get an API mismatch.

[Multiverse-Core] Enabling Multiverse-Core v2.5-b699
[Multiverse-Inventories] Enabling Multiverse-Inventories v2.5-b403
[Multiverse-Inventories] Your Multiverse-Core is OUT OF DATE
[Multiverse-Inventories] This version of Multiverse-Inventories requires Protocol Level: 20
[Multiverse-Inventories] Your of Core Protocol Level is: 19
[Multiverse-Inventories] Grab an updated copy at:
[Multiverse-Inventories] http://bukkit.onarandombox.com/?dir=multiverse-core
[Multiverse-Inventories] Disabling Multiverse-Inventories v2.5-b403

got the hang on it.