Video shakes

Hello I'm new in kdenlive but I have used many times Sony Vegas to do my home videos without problems.
I'm putting photos in the timeline and adding a composite transition and then I change the size of the clip (first it's 100% and in the end of the clip 150%).
So all its right but when I play de result the video shakes while playing. I have rendered the video and it shakes too.
I'm usin version 0.8.2.1 and linux mint.
Someone knows where is the problem?
Many thanks.