We have added a new feature since you last played with Context Free: the z-axis. In addition to moving shapes around in the x and y directions you can now move them around in the z axis. This doesn't change where they draw or how they look, but it does change which shapes are drawn on top of which. Your cubestack shapes works better if you dictate which cubes are on top and which are behind:
startshape CUBESTACK
rule CUBESTACK {
CUBE {s 0.5}
NEXTCUBE { x -.42 y -.24 z 1 }
NEXTCUBE { x .42 y -.24 z 1 }
NEXTCUBE { y .48 z 1}
}
rule NEXTCUBE .33 {
CUBESTACK {}
}
rule NEXTCUBE .67 {
}
rule CUBE {
SQUARE [r 15 skew 15 15 x 0.5 y -0.5]
SQUARE [r 135 skew 15 15 x 0.5 y -0.5]
SQUARE [r 255 skew 15 15 x 0.5 y -0.5]
SQUARE [r 15 skew 15 15 x 0.5 y -0.5 s 0.8 b 0.4]
SQUARE [r 135 skew 15 15 x 0.5 y -0.5 s 0.8 b 0.8]
SQUARE [r 255 skew 15 15 x 0.5 y -0.5 s 0.8 b 0.6]
}