I guess the next thing to try would be to comment out the style.css in the style.config file of one of the affected skins to verify that it is caused by the artisteer css.
I might also try removing this from the layout.master to see if the javascript added by Artisteer is a factor:
<portal:SkinFolderScript ID="sfs1" runat="server" ScriptFileName="script.js" />
I appreciate you taking the debugging steps since I don't have an installation where the problem happens.
Another thing that would be worth trying, we use the same css in the editor as in the page but there is a web.config setting that can specify an override url for editor css
You could put an empty css file in the root and point to that like this:
<add key="EditorCssUrlOverride" value="/emptycssfile.css"/>
If that solves it we can be sure it is caused by css and then we can try to narrow it down and override it in style-artisteeroverrides.css
To narrow it down one could go through style.css and start commenting things out until it is fixed and put things back until it breaks again, that approach should be able to find the specific part of the css that causes it.
Thanks,
Joe