Why does setting InverseMass to zero on a single particle freeze all particles?

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Hi there,

I'm trying to completely freeze some particles while making others still simulate. I adapted the script from (http://obi.virtualmethodstudio.com/tutor...icles.html) to target certain particles and stop them completely by setting their inverse mass to zero.

But what I'm finding is that any particles that come into contact with ones with inverse mass to zero come to a complete stop as well.

This even happens if I only set the invMass to zero on a single particle:

Code:

actor.solver.invMasses[0] = 0;

I'm guessing if a particle touches a particle with infinite mass, something bugs out and causes everything to stop?

Here's a gif of one emitter shooting a stream onto currently frozen particles. As soon as the stream touches those frozen ones, they all freeze. Hmm. I would have expected the red stream to just collide ontop.
https://gfycat.com/tarttartcockatoo

Thanks for any insight!