I am working with interlaced content. I have found that when working with sequences content will look fine in the program monitor but when I click within it I will then see interlaced fields. You know you have clicked or focussed on it becuase you see a cross overlayed on to the program monitor window.
Is it the case that when you focus the program monitor you are seeing both fields?
I have looked for clarification in documentation but cannot find any reference to this.
I'm assuming you're referring to the drop in resolution--perceived or actual--in the Program Monitor when you've selected, say, the Motion effect direct manipulation controls or clicked on the image in the PM. It does appear that Premiere Pro switches to a single field preview in that case, but I think what you're also seeing is PPro "gear down" and uses a faster but lower-quality scaling algorithm for easier manipulation of the image. Check out this blog post by Todd Kopriva for a look under the hood regarding scaling in PPro: some details about scaling in Premiere Pro CS5 and CS5.5 « Premiere Pro work area
Theoretically, this is done to make manual positioning/scaling/etc. of an element in the Program Monitor smoother and have more instanteous feedback as you manipulate the element. In practice, it can be a bit disconcerting because it does make exact positioning more difficult.
I'm not sure if I'm getting at the core of the issue you're posting about, but if not, post back; sometimes the engineering folks wander into threads like this and offer some interesting insights (as Steve Hoeg did in your 2:2 pulldown thread).