The quota of some users (i.e me, Lars) is updated to zero whenever they log in. In get_user_attribute() function, the quota is set equal to the mail of the user (mailMapping) and as a result the update_quota() function converts this string to computer file size (thus to zero).
Also, I think that this function should not convert to computer file size because the quotas are stored as human file size in the db table (this is also a bug in owncloud's app). I am not sure why this function is called with login on test. This is not the case on silo.