Thank you for writing to us.
This is not a bug but a deliberate decision - the amount on the right of the account row will always display current account balance. We've been discussing this and consider this to be the best decision.
To get the balance for a particular date please mouse over the period on the graph and use the pop-over that appears.
Thank you for your feedback on this :) I'll make a note of your comment and we'll monitor how many users write to us about it before we decide to make a change.
I agree with Pawel, I want to know how much I have spent last month from my different accounts.