This has to be the most annoying thing in iMovie. I just want a simple picture in picture. But iMovie crops the image and scrolls it!
I can't find any option to avoid this!!!
This could be due to a variety of issues and due to lack of details I don't exactly know what the problem is. So, instead I am going to answer your original question: How to put a picture in picture without any animations?
Select footage x
Select the second icon from the left in your effects toolbar (when you hover it should say "Video Overlay Settings") (I say second because, although not shown in the picture, there is a wand enhancer icon before it.)
Picture in Pictureis selected and the transition time is set to
Select Footage Y and repeat steps 4-5
This should create a picture in picture effect without transitions or zoom-ins.
Images and References: