This bug was actually already present in DT2 (sorry for not reporting it previously):
I have a PDF containing one or more A4-sized page(s) and one page sized 101*54 mm (packing label) in the last position. I view the document and set the inspector to thumbnail-view. If I now want to select the last page (the small one), I cannot. It highlights momentarily, but the highlight then reverts back to the page above (the larger one). Right-clicking the last page does bring up the context menu, but anything I select applies to the highlighted larger page. The only thing I can do is grab the smaller page and move it to any position other than the last one - at which point it behaves like any other page, can be selected etc.
If the last page is in portrait (i.e. 54*101 mm) it also behaves like any other page. So the problem seems to be a required minimum document height.
