The segmentation utilities check list states, that the radius slider is disabled when "Cross" is selected as option of the "Structuring Element". This is correct, but we think that this means: The radius has no influence for the "Cross" element.
However, if you change the radius in the "Ball" mode and then switch to the "Cross" mode, the current value in the disabled radius element still has influence on the calculation.

You can check this by creating a simple segmentation mask.

• switch to the segmentation utilities view and open the "Morphological Operations" widget
• check the "Cross" button (the "Radius" slider will be disabled) and hit "Dilation"
• notice how the mask will slightly grow
• now check the "Ball" button and change the "Radius" to something above 10
• check the "Cross" button and hit "Dilation"
• notice how the mask will grow significantly