Not a bug, just a weird little inconsistency that pops up when you use an “alternate attribute” with the “Multiply Probabilities” setting.

If you create a primitive attribute (say, called “density”) and vary it between 0 and 1 on a single polygon (where the remaining polygons in the model are set to 1), points pop in and out on polygons other than the one being changed.

I've attached a hip file that demonstrates this behavior.

As you scrub from frame 1 to frame 100, the density on a single primitive (prim 0) is animated between 1 and 0.

I would expect that changing density on a single primitive would not affect any other primitives. But for values other that 0 and 1, it does.

cheers,
-Mark