NSButton drawing glitch

FROM : Steve Israelson
DATE : Tue Jan 15 22:00:10 2008

I have a custom view that draw a rounded corner rectangle.
This view is NOT opaque.
Embedded within this view is a standard push button.

I have my NSWindow background color set to [NSColor redColor] so I can 
see what is being drawn.

The NSButton, when clicked, always shows little rounded off corners in 
red, ie the window bg color.
It looks like somehow the NSButton is NOT letting any of its subviews 
draw, but just in those corners.
The corners are NOT related to the button visual representation in any 
way that I can tell.

I can not find any way to make it stop, except to make my view opaque. 
Doing so of course messes up MY rendering of rounded corners.

Does anyone know how to make the NSButton behave?

I suppose I can nest an opaque content view inside my view, but that 
won't work if I use a fill color with an alpha value.