Gar, I did find the same issue day 1, but there is an easy workaround. The guys from SPT actually emailed with their take on this and they are right. This is the way to go, in their own words (and I do concur. Give it a go... it works fine for me now): 
 
[i]As you are probably aware there is a simple trick to working the buckles effortlessly. 
A simple set of guidelines that I use - 
 
1) Pull strap tight ( The buckles are difficult to lock when not under 
tension). 
 
2) Let go of strap end at the same time Pull clasp foward (The buckle now is 
under tension and the clasp will come forward easily). 
 
3) Hold clasp forward and turn key.[\i]