Weight Painting Problem on Mesh Clothing

I’ve been working on a dress (for Second Life) for the last couple days and finally moved onto weight painting. I seem to have a problem though, as no matter how heavily I paint on the dress under the arms, it just won’t move correctly with the body. I can’t edit the mesh of the dress directly as that would ruin the shape in any other pose.

In an attempt to try and find a solution myself, I ended up going against most tutorials I’ve seen and unchecked vertex groups on the armature modifier and checking bone envelopes instead, It fixed the underarm issue immediately, but it seems any weight painting I do without vertex groups checked, has no effect. Having both checked just brings back the initial problem.

I can hide most of the body with an alpha clothing layer in SL, but this particular problem spot wouldn’t work too well if I did that. I’ve also seen other similar items by other creators that didn’t have my particular issue in their finished product, so there must be a way to fix it. Which is what I’m asking now.

Here’s a couple screenshots of the problem:



Seems you’re a lot further into Blender than me - but I’m curious. Is there any chance the top part of the dress is also controlled by other Armature parts? I know that sometimes a control by Armature with Automatic Weights can do some strange things. So if - for some crazy reason - the top of the dress is 20% controlled by the right foot (and the foot is staying still in your screendump situation) it would counter-effect your bending along spine/chest?
Just a shot.