In the VPX16 user manual it mentions : Interpolation for interlace footage along with Anti-interlace filter and Border cropping adjustment in the object context window.
But when I look at the VPX16 context menu it only contains Anti-Interlace filter and Border cropping adjustment.
Conducting a search on the forum, I did find reference to this feature in an older version of the program.
The first option if I am reading it correct would only apply to video footage so that if a still was taken from it you would not get a mismatch of top field vs bottom field. For video that option appears when choosing 'Properties' from the drop-down list when you right click. The option is not available for stills as they do not have top and bottom fields.