I had the same issue with CG Raster Data memory increasing by simply pushing and popping a view controller repeatedly. I spent a while thinking it was an issue with some drawing code. I finally tracked it down to a delegate not weakly referencing the view controller that was being pushed and popped, so when I popped the view controller, it wasn't being deallocated. The CG Raster Data happened to be the biggest part of that view controller's footprint, so I mistakenly attributed the problem to that initially, when it was really the view controller itself that wasn't being released (therefore, not releasing its views, some of which had CG Raster Data).
In short: if you're seeing memory leaks with CG Raster Data, look at view controllers that might have views with them, and make sure that they are being released.