It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
We have also done this in order to create a stable thrust in a predictable direction. This was done to resolve a chronic problem with axial shuttling. For your pump, it was most likely done so that your mechanics are less likely to install the impeller backwards as 1gibson noted.
