I think I know what you are seeing and it is definitely a usability issue. In the Android App, say you pick a past month and you see a list of expenses in the past month (in your case, there was nothing and so the list says, No expenses found), now you click Add and here the default date is set to today (present month), you save your new expense in the present month, it gets saved, but the list still shows the past month and says No expense found. I think the right thing would be to show the list for the month the new expense was added to and that way, the user sees that the expense entry was indeed saved.
Is this what your scenario?
But like you said, in the Online mode, nothing gets saved in your phone and since you see the entry in the webapp, the entry was made.
