Hi all,

In Houdini 22.0.466 I’m merging four RBD setups (shingles, drywall, stone, wood): 18k pieces and 68k Glue constraints. Every time I change the Merge input order, I get a different simulation. Each result looks plausible, but they’re clearly not the same sim.

I checked the solver inputs per piece name and per constraint pair. Apart from element order, they’re identical between orders. Names are unique, there’s no anchor_id, and there are no detail attributes.

I attached two flipbooks: same setup, different merge order. If I keep the merge order and just reset the sim, the results match exactly.

Is it expected that Bullet gives different results purely from element order?
What’s the best way to make it reproducible (sort by name, Randomize Constraint Order, more iterations)?

Happy to share a .hip. Thanks!