I ended up using the Intel SVTools to inspect the MAC management registers. The crucial bit for my issue was the OS2BMC Enable (MAC Management Control (MANC) register bit 28), which for some unknown reason was set differently by default on a system using an I350 controller and another system using an X540 controller. Now I just have to figure out how to get it set consistently on both systems.
- Julian (not really that weird ;-))