I tried to change the sorting order on the "Sort by Fields" dialog and noticed that on the third field and the ones below clicking the "Direction" does not change from Ascending to Descending. I tried this in many different reports.
Valentina Studio Pro 7.5.8 (64-bit)
OS X El Capitan 10.11.6
iMac (Retina 4K, 21.5-inch, Late 2015)