Ok, we've finally nailed it.
The issue was that the server B returned "i'm at 127.0.1.1" on the first IIOP-request (context-listing) from server A. That way, server A requested the remote bean to 127.0.1.1 which it not could find because the bean was not deployed on server A (only on server B).
Sniffing on the network gave us the solution. We resolved this by changing the etc/hosts file on the Ubuntu server (and removed the line where '127.0.1.1' appeared).
This is, i think, a bit of a bug, and should be somehow configurable in Glassfish, so that you can decide on which interface Glassfish should be working (changing it in the admin-console, under IIOP-listener, from 0.0.0.0 to the correct IP-address did not solve the issue!).
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