It was a while ago, but I have seen this for dates in British Summer Time on a SharePoint server where Windows was configured to not obey daylight savings. This resulted in the indexed datetime - which was a date-only field, and therefore stored as a datetime with 0000 hours - having an hour 'removed' from it. Thus, a date of today would be stored as 2013-08-08 00:00:00, but be indexed as 2013-08-07 23:00:00.
The clue to this was that dates outside of summer time worked correctly.
If you can, check the full value for the date in your managed property, including the time portion.