This was due to specifying negative source coordinates for the texture copy, which must lie within the bounds of the source and destination textures.
The behavior now is to clamp the copy region to [0 <= size <= backbuffer size], resulting in a copy region that can be smaller than the backbuffer, but never larger.
Since ResolveSubresource cannot be used with depth textures (and throws an error with the debug layer enabled), use a shader which selects the minimum depth value from all samples.
Changes the sampler by XFBEncoder to use a linear filter, rather than point, to match GL behavior.
Stenzek