Hello,
the ytheme-aero.css uses the same background img for grid and panel. That looks a bit confusing when using a contentpanel with a grid or gridpanel. This is not the case in the default theme.

Code:
Grid: x-grid-header
background:transparent url(../images/aero/grid/grid-hrow.gif) repeat scroll 0%;

Content-Panel-Header: x-layout-panel-hd
background:#EBEADB url(../images/aero/grid/grid-hrow.gif) repeat-x scroll 0%;
So i would suggest to have different bg images.