VTK (and by that, MITK) lookup tables are not used (displayed) anymore. An image with a valid lookup table and "LookupTable" property is still shown as gray value.
(For some details see report from Claudia Haenel from Okt 26 2010 on users list).
Can be reproduced e.g. with ShapeBasedSegmentation on 4D images: Segment 4D image, use button "Show inner motion". LUT is not used.