Rigged mesh vertices go crazy or break (no shape keys)...

(Posting this here because I am not sure whether this would be a Mesh or Animation problem…)

Hello. I’m trying to make a very basic skirt (as a test) for a premade mesh model. To be more specific, it’s a Second Life avatar, which is “Fitted Mesh” that I am trying to learn, I am not sure what the official term for that is outside of SL, but it’s basically to make sliders in Second Life’s appearance editor deform the mesh’s shape beyond stretching the basic skeleton bones (such as the waist size, butt size, etc).

So, the problem I am having… is that the skirt mesh is for whatever reason, doing umm… I have no idea what it’s called, but it’s like the vertices just all become jagged and go nuts, a phenomenon that I’ve only otherwise encountered when editing the vertices of a mesh that already has Shape Keys, which was solved by deleting the shape keys… but this skirt has no shape keys at all (or at least not listed under “Shape Keys” where they normally would be, so I’m really not sure how to fix this. Or if there’s something else known to cause it, whatever “it” is called?

For visual reference, this is what’s happening. By default it looks like this:


When I alter the “fitted” shape slider of the “Saddle Bags” (side of hip/leg width), or any slider for that matter, it does this:


So, even if you don’t know how to solve it, is there at least a name or term for this kind of thing the vertices do?

Displaced vertices is all I could think of as of right now as name for this type of problem.
Here’s the following things you should, check If the skirt object has any modifiers applied to it, if it does have any, deactivate one by one to see which one could be a potential trouble maker for this mesh anomaly. Second, go into edit mode and select everything with ‘A’ key and press ‘Crl + N’ to normalize the vertices. Third, I honestly don’t know, you should check how many vertex groups you have for that skirt mesh object and see to which bone which vertex group is assigned, if you have different vertex groups that are assigned to bones on the opposite side of the model that could be a problem.
If you really want us to help you, you could upload your blend file here: website and we(the community) will personally look into the file and try to solve your problem as well as give you an insight of what has caused this problem and what you need to watch out for next time you do a similar project.

When you’re on the provided site and once you upload the file don’t forget to copy the URL generated after the upload so that you could post it on this site.