There are many things that effect the stall read the section on turns most notable the descending turn. http://www.experimentalaircraft.info...ll-speed-1.php

How steep was the turn to final look at the chart a 60 degree turn would double the wing loading increasing stall speed to 1.5 times straight and level. The weight of the remaining fuel would be equivalent to 1.5 times full tanks. Might this contributed to the snap?

If you were in a descending turn and changed the attitude of the aircraft by trying to level out that would increase the stall speed as well. Any pitching up moment increases the wing loading. Lots of combinations in fluid dynamics that affect the stall even well above normally experienced stall speeds.

http://en.wikipedia.org/wiki/Stall_(fluid_mechanics)

Without observing the flight we can only second guess and offer possible ideas to help you try and figure out what caused the stall.

Dennis