Hey there,
I have a window with a backbuffer and it's doing something strange and I don't understand how.

When I present the backbuffer to the window it has a dark grey border around the edge of the client area, which is being produced by the backbuffer.

I cannot figure out where this border is coming from. It doesn't make sense because my BitBlt() is:
(Where the backbuffer is the same demensions as the client area)

The border is equal all the way around the client area, which is the most confusing of all. If I had simply got the width and height of the client area wrong, it wouldn't have an equal edge all the way round...

Here's a image of the window:
http://i233.photobucket.com/albums/ee74/Lightfooted/Public/windowError.jpg

You'll notice the slightly thicker than normal client area border.
What could cause this?

You're not drawing to a control or anything that has a border style?

How are you clearing the backbuffer?

After fiddling around a bit, I found I had to increase the size of the backbuffer to two pixels larger that the client window in both demensions.

And then:
Strange.

I do seem to remember something about the client area always being +1 in both dimensions, when you retrieve the client area.

Why is that the case?

It's probably just for convenience.

But this is not normal behavior, so I suspect there's something wrong elsewhere in your code.