I think it's normal. The alignment of the retarderlayer is really critical since it must be placed exactly in position. What i've heard it seems like the phenomenas are perfectly normal though.
Mb: Asus P5W DH Deluxe
Cpu: C2D E6600
Gb: Nvidia 7900GT + 8800GTX
3D:100" passive projector polarized setup + 22" IZ3D