System Information
Windows 8, AMD 7950

Blender Version
2.73 offical

Short description of error
In the example you will see a red sphere in worldspace and its screen space position returned with getScreenPosition.
Ive set up a 2d filter which renders a white circle over the top and set to the position of the red sphere underneath using getScreenPosition. You can use the left and right arrow keys
to move the red sphere left and right you will see the white circle over the top lag behind by a few frames.

Ive purposely set the framerate low to make it easier to see as you move the sphere but it happens at high framerates to. Im thinking its either 2d filters and passed in uniforms not being updated correctly or it is infact getScreenPosition's problem.

Oh and same thing happens if I calculate a 3d objects worldspace position to screenspace myself using gluProject, so maybe not a problem with getScreenPosition?

Can anyone shine some light on the issue?