i have seen the same thing happening, but normaly when it failed to update it just started the program without the update and it worked fine. I then closed Achat and started again. It repeated the update and this time it came to the end.
I had have it happend to me before, so i don't know if it is a common thing. I Just know i have it not with every update and it started for me some week ago. The worst i had was when it tried the update for 4 times before it got trough, but it always did in the end.
So my advice, if the update does not work the first time, close the achat back down and restart till it works. For the rest it's up to the dev team to find out whats going on.