I tried copying your control.xaml over mine and it didn't actually do anything, so I then tried renaming ParameterWindow.xaml to .xaml.old as clearly the theme was overriding the styles, but it's being called from somewhere (I couldn't find where on any of my other .xamls) so fails if named like that.
I know it's really cheeky but I'm wondering if you could cast your eye over my theme (mainly Parameter.xaml) to see where exactly I'm going wrong. You'll probably groan at my mistakes of coding, but I'm a big of an .xaml beginner

Here's the theme: http://www.ilovecubus.co.uk/pete/cubus_1468.zip