I used Jgnash v1.13.0 through fiscal 2013, and have recently moved to Jgnash v2.15.2 to work on fiscal 2014.
Running the balance sheet report for 2014 has most accounts showing a value of zero in most months. I've now replicated a report that I had done for 2013 to determine the problem.
In reality, the balance in an account (e.g. accounts receivable, bank) is not zero. When there the report shows non-zero, it's not the balance in the account, it's the total of the activities that month.
Of course, I can go back to the account register, and see that the value in an account is non-zero.
If it makes a difference, my data files were XML format in Jgnash v1 and now XML format in Jgnash v2. I'm using Oracle Java 7 on Ubuntu 14.04.