problem transferring vignette effects from Color to FCP

Hi, I am having a real problem with some of my clips being stretched when I transfer my FCP footage back from Color to FCP after it has been color corrected and rendered.

When I send the sequence back to FCP and view it on my timeline, some clips have been stretched and it appears as if the aspect ratio has been changed in some way, I originally thought this might be a problem with the whole sequence but only the clips that I applied a vignette to in Color have been affected in this way, all other clips that I did basic grades on appear to be fine and the image is not stretched. Therefore the only reason I can think of is that it is a problem related to the vignettes I have applied in Color that has resulted in the image being distorted and stretched in FCP.

I wondered if anyone has encountered similar problems when they transfer their footage back from Color to FCP? And if you could help at all with this problem as I'm really stuck.

Thanks in advance

Spencer