It's funny this thread should come up because I am experiencing the exact same problem with a Realforce 87U and the Mac Mini I use at work. A key press works to wake the system from sleep, but after that the board just goes dead. However, clicking the mouse button to wake it causes the keyboard to function normally.
Since it seems to affect both the Realforce and HHKB, there must be some kind of firmware issue. I could use a key press all day long with the Filco I had connected to the machine previously. In the end, it's not a huge deal to use the mouse, but it would be nice if there were some kind of permanent fix for the keyboard. For the joy that typing on the Realforce brings, along with my much improved accuracy, it's a compromise I'm more than willing to make.