In Symfony 1.4.x I found I was missing stylesheets for the admin generator pages. Specifically, I was missing the following:
<link rel="stylesheet" type="text/css" media="screen" href="/sfPropelPlugin/css/global.css" />
<link rel="stylesheet" type="text/css" media="screen" href="/sfPropelPlugin/css/default.css" />
It took a bunch of digging, but I finally realized there is now a sf command for ensuring these are in place:
symfony plugin:publish-assets