Yep, I read your posts, and I’ve experienced exactly the same thing. But whether or not it’s a bug isn’t necessarily dependent on unexpected behavior, but more often on non-functionality, which isn’t the exact case here.
My post wasn’t to disagree with your assessment as much as to caution you against expecting it to be treated as a bug. The hair particles system functions, and within limitations we’ve both stumbled on, it functions quite well. The devs may consider that perfectly adequate, and not put much effort into making it work differently so edits to the emitter mesh are more forgiving. It may even be that the overall topology of the mesh in terms of vertex count is essential to the proper functioning of the hair particles as they are now implemented. I can’t say for sure because I didn’t write the code and have no interest in digging into it.
What I can say is that if it’s reported as a bug (and I’d encourage you to do so), it may be “rejected” for attention simply because it could be considered as simply a limitation on using the system. I had this happen when reporting that the hair did not properly respond to standard lighting techniques, went through a week or so of testing and documentation to back it all up, only be told that it’s simply a “limitation,” not a bug. So it goes. I found workarounds.
One workaround you might consider (if indeed the potential bug isn’t addressed) is to always use “wig” meshes for hair particles, simple meshes that will need not further vertex-count editing once made, that can be linked to the main mesh many different ways depending on the need for movement with certain poses, etc. I did that with my current model’s head of hair (a good thing) but not her eyebrows, which wasn’t so good, but I wasn’t aware of the limitation until long after I’d finalized too much to want to change that hair system again.
Bottom line, we both agree that it’s not “right” that editing the mesh in certain ways, no matter where, will jinx the hair particles, but our dissatisfaction may not be enough to justify a bug hunt, because the hair particles do work well within that limitation. Just a heads up that may head off some frustration if you decide to report it as a bug.