Still images get interlaced

Hey!

I'm editing a short hd video and if i add motion to still images, they get interlaced. Tried de-interlacing (upper, flickered, etc) but didn't help. What could could be the solution?
Thanks

Is the Timeline progressive or interlaced?

Well if U mean the sequence, it sais that the field dominance is set to upper, so i think its not progressive, but the sequence settings are automatically taken from the video file(s) (they were shot in the same format). But the videos are ok, only the pictures are interlaced (during playback and also after exportation).
Here's a link of my video by the way:

I can only see one problem: in the split screen at 41". And that's not really an interlacing issue. Select the still image you have animated in the split screen and press the Info tab in the Inspector. Top left in the Info panel you will see the name of the clip with the date the clip has been created. Under this you will see the frame size. What is the frame size of this clip?

Actually that part is taken from another motion picture, but is enlarged and slowed down. What I'm thinking of is at '22 and '04 (where the split screen goes out). I the issue is only visible at bigger resolutions (480 p and over).
And by the way the problem you've mentioned - I think it's because the picture is enlarged (about 200%).
Thanks anyway