Dont know if this will answer your question but whenever I add a new item to inventoria it wont show up in express invoice.
Bit of a pain when you do an invoice and the new item you just added isnt there.
What I do in this situation is go to items list in express invoice, delete everything and then click on the migrate from inventoria option.
This brings everything over from inventoria and you are then right to go back into invoicing and type away.
I also found if you try to add an item that is zero stock in inventoria the whole thing crashes so its a matter of shutting down express invoice, adding stock to inventoria and then going back to express invoice, deleting everything in the items list and do the migrate thing again.
Hopefully these issues will be adressed in later versions.
I am running Inventoria version 3.37, Express Invoice version 3.71 on a Mac Pro OSX 10.6.8, in Rosetta