Apparently the implementation of Dicom tag extraction implemented in MITK does not support subgroups. GDCM (and itk) seem to handle the subgroup tags equally.
But if a tag for example "Pixel Spacing" (0028 0030) is not located in the main dicom header but subcategorized by a certain subgroup, MITK does not recognize it anymore which leads to misinterpretation
(see T23537-support-dicom-spacing).
So the question arises if and how we want to add subgroup handling?