My guess is that somewhere in the chain, you converted/imported interlaced footage to progressive and from there it can’t be recovered as interlaced. Have a look at your workflow from beginning to end. When PPro converts from interlaced to progressive it seems to throw away half the vertical resolution by leaving out one of two fields. Other programs such as AE, Shake and others give a choice of interpolating, duplicating etc. Makes a big difference in quality.
http://www.postproduction.be