For our set of growth parameters perfect, 4H-SiC can only be grown in a small temperature range of about 25K. The upper limit of this range is given by the 6H-SiC stability region. Below this temperature range, 4H-SiC is prefered too, but the grown crystals are disturbed by hollow slits often penetrating the whole crystal. The average slit size is 1-10mum in width and 1-15mm in length. The lateral slit extension is preferentially aligned in [1 (1) over bar 00] and [11 (2) over bar0] directions. An explanation is given based on the theory of van der Hoek et al. [1] derived from the BCF theory which enables to interpret developed step pattern on growth interfaces.