Masks creating lines.

Hey all,

Making this 'fractured' text affect in AE using shape layers as alpha mattes and displacing the text to create the following affect. For some reason, the masks are creating these thin but noticable lines. I've not been able to figure out how to fix this. It only seems to be caused when used in a pre-comp and rasterized. Within the comp itself it's fine, no lines. But want to use it in a precomp to keep the project neat and also to help with other effects / keyframes. 

Any help with this would be huge. 

Thanks a lot.