It seems that this behavior is caused by the newly introduced HideFreeCells property which was not accessible and was always set to true.
HideFreeCells="true" hides non-business hours (outside of BusinessBeginsHour - BusinessEndsHour range) if there are no events.
This property is now accessible in build 6.6.2342 - see also http://www.daypilot.org/daypilot-pro-6-6.html. The default value is set to false.
Please let me know if the problem persists with the latest build.