Aliasing when shadow filter is applied

I'm seeing some significant aliasing artifacts when a DropShadowFilter is applied to a sprite, unless cacheAsBitmap=true. Normally wouldn't be a problem as I'd just cache it as a bitmap, however I'm seeing some display bugs related to using it.

1) has cacheAsBitmap=false, no shadows

2) has cacheAsBitmap=true, drop shadow

3) has cacheAsBitmap=false, drop shadow

Am I doing something wrong or do I need to do my own shadows?