Cubase 6 as MTC slave doesn't stay in sync

I have Cubase 6.0.4 on my main machine. I’m writing to film, so I need to sync video. I want to play my video on a second computer. I have no S/PDIF, so ‘VST system sync’ is not an option. So I have a copy of Cubase Elements (6.0.4) on the second machine as an MTC (Midi Time Code) slave to host my video.

If I move the cursor on the Master machine, the cursor always dutifully moves to the same frame on the Slave. And as soon as I press stop the Slave always stops at the same frame as the Master. And for a while the Slave correctly stays in sync during play. But over a work session, eventually when I press play on the Master, the Slave will jump ahead and play a second or two ahead of the Master (the amount varies). I’ve seen it as great as 5 seconds.

Restarting everything (ugh!) seems to temporarily fix the problem.

Frame rate is the same on both machines (25fps), same as the video.

When the Cubase Slave has exhibited this behavior, I’ve exited and fired up Sony Vegas as the MTC slave and it syncs correctly, so I suspect the problem is on the Slave end instead of the Master. But that’s suggestive–hardly definitive.

I have XP Pro on both machines, 64 bit on the master, 32 bit on the slave. All the latest SPs, of course. I’m using ‘Midi over IP’ as the midi link between the machines.

Yes, it’s definitely the Slave. I only have to restart the Slave Cubase for things to work correctly again.