First idea is to post the file so someone can take a look at it.
Second idea is to pose the mesh so you can see the problem while in weight paint mode, then tab into edit mode. Now select an offending vertex and look in the transforms panel, you should see what vertex groups the vertex belongs to and the weight of the vertex in each group.
It is possible to weight a vertex 100% to several bones. But obviously this can’t work, a vert can’t be weighted 100% to 2 bones, so in the end it’s weighted 50% to one and 50% to another, but it will appear weight 100% in the view. There is an option in the menus when in weight paint mode to auto-normalize the weights of the entire mesh, which adjusts the weights to their actual values. Additionally, when in wieght paint mode, always enable auto-normalize in the tools panel, this will auto-normalize the paints while you work.
If this doesn’t help, go with my first idea…