Same issue here.
Running 3.0.4 (didn't work on 3.0.3 either which is why I updated hoping it would be fixed)
Placing an item onto the left side does nothing. Placing an item in the fire destroys the item without changing the EMC value or interface. Placing an item in the target slot, again, nothing. Stuck on "No Lock," no matter where I place items.
I've tried destroying it and replacing, reloading the server, stopping the server and rebooting, taking out plugins 1 at a time and altogether to see if the issue lies there but nothing changes. No error reports, no logging, zilch, nada, bupkis.
Plugins:
Multiverse (core, inventories and NetherPortals)
DropClear
CommandBook
WorldEdit
MineBackup
How we doing for answers on this one?