distributed rendering slows down after a couple of frames

[leabum]

I am rendering hair over the network on a couple of machines with distributed rendering inside of the framebuffer so that I can see what each machine is doing (The PC's name is displayed in the renderbucket it is currently rendering). It first transfers the frames for the specified framerange to all the machines and then renders like the first 2 frames on the mainmachine only, until the slaves finally start rendering buckets also. Of course rendering goes very fast then, but after a couple of frames the slaves stop working it seems and there are only a few buckets wich are being rendered at all. The name of the buckets says 'workstation' which is my mainmachine I guess I started the render from. The CPU is only being used to 1% on this machine which is why those few buckets take years to render and really slow down the process.

What can cause that? Why is the CPU running so low and why are no buckets assigned to slaves anymore?