Because the actual display mode is always forced to 32 bits color depth,
surfaces that would be created without a pixel format need to be explicitly
set to the emulated display mode's pixel format that the application expects,
rather than letting them use the actual display mode's pixel format.
However, the emulated pixel format was being forced on surface types that aren't
normal surfaces and shouldn't inherit the display mode's pixel format
(e.g. vertex buffers and depth buffers), which prevented some of these surfaces
from being created correctly.
Now the surface type checks are more restrictive.
The palette converter surface was being released even when it was null,
leading to potential problems with releasing the primary surface.
The update thread is also no longer terminated on each release.
Termination may have been necessary more often than expected because
the thread may be waiting on the DirectDraw critical section on release.
There doesn't seem to be any issues with letting the OS clean up
the running thread on exit instead.
