Create a report set with a report of type 'Analyis Table' and set it up on metrics from 'User Session' times. It will show you the last "good" interval plus one interval in the future that is not fully completed yet. For instance if you look at 'Last 12 months', it will show you August and September. And if you choose 'Last 7 days', it will show you the 13th and the 14th (even though the 14th isn't yet over--date is Sep.13th).
Software Defect. This issue is being tracked as FXM-390
The 'Last full Hour|Day|Week|Month' timeframes are not affected by this defect. Use those instead for now.
Waiting for fix in a future release of FxM