I do not see the problem you are talking about, it seems that you want every part of your theme to blend together!
For example the toolbars, TCP, transport & MCP to not show where they start and end (No Borders). If that's what you mean, then I see the line.
It should be there, Theme Designer's should be able to change it.
I think it is not a bug and this post should be moved into the correct area!
Robert