procoder is locked to frame structure?

ok I dont know whats going on here, but I encoded a few things a few months back using DVD2SVCD and I could encode using ProCoder, and I could set the picture structure to 'always field structure'.

now I encoded something last night and set the picture structure to 'always field structure' and when the encoding finished, I checked my file using bitrate viewer and it said that the file was in 'frame structure'.

could someone tell me why this is happening.

im using:

* DVD2SVCD 1.2.1 B2
* Canopus ProCoder 1.01.35.0

Video source is Pure-Interlaced (Video)