You are most likely looking at an MRR view report rather than a revenue recognition view.  See Difference between Revenue Recognition and MRR. 

In the accounting view, the system rounds to the nearest month for any contract value which is less than 10% of the days in the month.  This is because often contracts which are intended to be for a full month are set to end or start a few days from the actual month end due to differing days in the months or other factors.  So if a contract is set to end in the first three days of a month, it will show as ending the month prior.  Similarly, if a contract starts on the 28th day or later of a 31 day month, it will not show in that month but will show as starting at the beginning of the month following. If this is not the case, then you may be looking at a report in full month view.