Many thanks Flick. Yes, when I change the BPM setting on the 22500 to match the imported rhythm loop BPM everything plays back as expected. It now seems so obvious … So there is nothing wrong with my looper.
That said, for my purposes (importing backing tracks to play over) it seems a little awkward to change the tempo of the 22500 every time I select a new track. Experimentation suggests that everything is ok provided the BPM of the loop corresponds to the current temp of the 22500. So would it make more sense to set the BPM of each imported loop to the same default value and then keep the tempo of the 22500 at this default value? Or, put another way, if you do this what are the downsides?