Was in the shop to purchase a darkness pack at the Gold level ($100);
I purchased a pack and got the cards, but when I purchased a second pack, I got the following message:
TypeError: undefined is not an object (evaluating 'card.element'),
http://etg.dek.im/etgify.js, 6422, 58
I didn't get any cards and it took my $100! - yikes.
Leaving the shop and coming back does not reset whatever is going wrong. Logging out and logging back in does do the trick though (and then I can buy at least two packs before it flakes out).
update:
I tried to purchase different packs and it seems that it wasn't a problem - is one of the darkness cards throwing an error?