This has happened with both P2 and Canon DSLR footage (H.264 in .MOV container). Most of my projects that I open up from CS6 have clips that are incorrect (zebra stripes on the block). From what I can tell, CC is interpreting the footage as starting later in the clip that it does, so if I double click on the clip in the timeline, and scrub in the source monitor, I can see the tail end of the clip right at the beginning. Opening these projects in CS6 works fine, but it’s annoying to have to keep CS6 on my machine just for these instances.
I have never seen this issue before, so I’m not sure what’s causing it. Is this something I should submit as a bug report?