What effects have you applied? For example, the Puppet Pin tool, perhaps?
Yep, the puppet pin tool - is that messing it up?
From the help file:
Don’t animate the position or scale of a continuously rasterized layer with layer transformations if you are also animating the layer with the Puppet tools. The render order for continuously rasterized layers—such as shape layers and text layers—is different from the render order for raster layers. You can precompose the shape layer and use the Puppet tools on the precomposition layer, or you can use the Puppet tools to transform the shapes within the layer. (See Render order and collapsing transformations and Continuously rasterize a layer containing vector graphics.)
I would suggest precomposing the shape layer and scaling it up as much as needed in the precomp first (making the precomp as large as needed) and then apply your Puppet tool and go nuts!