So yesterday I was working on a deck in the premium deckbuilder and when I hit the "achievements" button, it crapped out and gave me a long string of php (?) code.
I was able to get back to the deckbuilder by hitting the back button in my browser and save my work. And the "check" button appears to still be functional. Also, when I go back to the "manage my decks" section and click on the deck list, the eligible achievements still show up, so the achievement checker appears to be working on some level, just not live in real time when you're editing.
This was on the 1e side. I haven't been into the 2e deck builder to check it.