I installed it into build 1380. I submitted my login informations. Then it gave me nothing. After browser restart, it's just showing empty popup page but number of unread items badge is true. Between readitlater moved to http://getpocket.com/
Yes, it was renamed to Pocket and moved to new web site, but it should work the same as before. Could you please post if there are some errors in error console just after opening the popup?
Nothing in error console about extension. (I tried with clean install to get an error several ways but nothing.) Could you try with Win7 Sp1, portable installation Opera 12b?