If you set Gallery's default sorting to be descending by date (in AdminCP), it'll work. But using the dropdowns at the bottom doesn't work to change the sort order, I think. (I think I reported that a while back.)
Ok, my admin friend fixed the mising code and the sorting works now.
If it helps, he said
I didn't have time to wade through all the code in browseimages.php tonight
to see exactly why the sort order wasn't being set, but I did create a fix
anyway. I checked $condition['direction'] (that's where the sort order
should be) and found it was blank right before the query, so just above the
query I added:
That fills in 'direction' with what you set it to in the request if the
code gets that far without setting it itself. It shouldn't get in the way
when the code sets it to DESC or ASC automatically for other types of browsing.