I suppose you know it already but just in case. In the file I provided, the red circle report a radius of 3.25 and when I select the "flower" it reports 5.8008, 6.5, 0.4375. This is with the latest beta of course.
Hi Felix - when you pick the flower it reports the bounding box of the flower, and since the flower does not have any geometry at the extreme positive and negative x axis locations where the circle does, its bounding box is smaller than the circle.
You can see this by selecting the flower and using the BoundingBox command - the yellow box show here are the bounding box of the flower:
Note there how the bounding box around the flower is smaller than the circle.
You were probably thinking more along the lines of a spherical bounding volume, but the one that MoI reports there is an axis aligned bounding box.
No problem Felix - I can totally see how it was easy to focus on the circle being a nice boundary for that shape, so it was natural to think of the other bounds as being the same.