ok, let's take the cineform codec as an example. How exactly do you get de-interlacing. First, you set your project settings to either blend or interpolate. Then, you hit "custom" in the "render as" screen. Then, what exactly do you do to get it de-interlaced?

For the Cineform Codec:
Under the first tab I use "Best" for the quality.
Under the "Video" Tab there is a fielding selection UFF/LFF/Progressive.
I choose the progressive for the fielding which is frame based.
If I then insert this cineform codec back into VMS 8 I need to assign the PAR to 1.3333 adjusting the properties of the cineform file in the project media bin, this is the bug you had pointed out where VMS isn't reading the file correctly.
If I then use this de-interlaced cineform file to create a new hdv.m2t file (which is a fielded file), the video is de-interlaced and the motion isn't smooth. I used a test video of some cars driving by to make sure I would lose the motion by de-interlacing it.

This also appears to work the same in VMS7_Plat (still on the machine).

That's how it's working on my machine with the cineformhd codec but in addition to manually changing the fielding selection under options I also have to have either blend/interpolate assigned as the project settings (note: a setting of "None" as de-interlacing method under "Project Settings" did not produce a de-interlaced video on my computer even after using "Options -> progressive" ).

If I use another codec such as hd-wmv the hd-wmv codec will de-interlace the video, same with hd-divx (but I don't use VMS to create divx videos, use other software which gives me more audio options for divx encoding).