Using FCP 6.0.6 on mac book pro OSX 10.7.5 Dissolves and Titling causing 'jumps' of images

Hello, Yep, so haven't edited for a few years, so haven't upgraded from 6.0.6, but suddenly require for project. Running fcp 6.0.6 on mac book pro (2012 solid state) with OSX 10.7.5. Generally found platform stable in past, but at the moment I'm having troubles with basic cross dissolves and titling supers - the image at the completion of the dissolve suddenly 'jumps' as it sometimes does at the end of a titling clip.
Clips are a mix of mp4 and .mov files that I'm washing through qt pro so all have same frame rates (25), aspect ratio (16.9), etc with codec as H.264 on hdv 1920 x 1080.
I'm completely lost as to why this is happening. HELP! Thanks