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Hair particle systems' caches vanishing
Open, Needs Triage by DeveloperPublic


System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce RTX 2080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 431.60

Blender Version
Broken: version: 2.81 (sub 14), branch: master, commit date: 2019-10-07 20:16, hash: rBa856c5eccffb
Worked: (optional)

Short description of error
As adressed in T70642 (but the report was split upon request as it turned out it contained two different issues).

When working with multiple hair particle systems on a same object, the baking process for one particle system will also bake the second particle system simultaneously. However, a click on the other particle system will permanently erase its cache.
It is even more evident when turning on Disk Cache and naming the two caches differently, the vanishing of the second cache can be witnessed in real time in windows explorer.

Exact steps for others to reproduce the error
Simply bake one of the two particle systems present on the object, see how the viewport is reactive once baked, for both systems. Then switch to the other particle system, and notice how when scrolling in the viewport, this particle system has to be recalculated.

Again, as stated in T70642, Bake All Dynamics cannot solve this issue as it has no effect on hair systems.