This sounds like it may be a mix of localised and non localised time zones being used. Is your local timezone 6 hours or more different from UTC? Just thinking 4 x 6 hours is 24 hours, so a day different.
That could be it, we are using CST which is 6 hrs from UTC, however it doesnt seem to matter what time of day you do this. It still keeps increasing the date fields in the search by 1 every four records viewed.
We are using the comparison under Add-on widgets, dates are localised.