Mesh Region in Emitter Switches Off Particles

I'm using a mesh exported via FBX from Lightwave's Modeler as a region in a pEmitter. The shot is 350 frames.

Between the 250 and 300 frame mark, all the particles die off. Now, this isn't me setting a keyframe to switch off emission or limit the lifespan. To test that, I tried other region types, and they kept emitting to frame 350. I replaced all the nodes in case I'd missed something, but it kept happening. The common denominator was the mesh. I tried a second and different mesh; same problem.

Any ideas what this might be please?

This is version 8.0 build 18.

Thanks.

I exported a cube from Lightwave, tripled, with a surface and UV. That worked. A tripled sphere, on the other hand, like the other more complex objects, still displays this killing of particles at frame 250, or rather it looks like no more particles are emitted.

This is about to cause some serious showstopping trouble on a job.

We thought about using a bitmap region as emitter, as a workaround; that seems to have similar problems.

Any help would be appreciated, or if these features simply don't work, which is what it looks like to me, I'd appreciate knowing so I can stop wasting time with this tool.