The Information Tab for HyperTreeGrids are incorrect
The problem with HTG is that the geometry and data is stored by HyperTree. The reason for that is within a parallel HyperTreeGrid, complete HyperTrees must stay together. So the reader and writer deal with things in units.
In the todd problem which is 12 x 2 x 2 there are 48 HyperTrees and so 48 DataArrays of "tev" and 48 ranges. So if you examine all 48 you will find the correct min and max as it appears in the UnstructuredGrid, but in different HyperTrees.