Final Cut Issues

Spent an age today trying to compile a demonstration video whereby some footage was 1080p ProRes from the Camera and others were MP4 screen grabs from Quicktime Player X. Firstly, I was unable to get the screen grab footage to load into Final Cut Pro, so I tried transcoding it to ProRes and HDV but neither of these would still load into FCP? Any way, eventually, after using EXPORT TO DV within MPEGStreamClip, I managed to get some footage to load. However, I didn't realise until after several exports of the finished edit, that my sequence preset had been set to PAL DV 720 x 576 due to the format of some of the clips being brought in. This was fine, or so I thought, because I could simply amend the sequence preset from within the settings window. After having changed the sequence preset back to ProRes(LT) 1080p 25fps, the strangest thing happened to all of my footage in that its dimensions drastically reduced, even for the native 1080p footage from the camera? To cut a long story short, the only way to get round this was to re-add each of the pieces of footage back onto the sequence? Very strange??