Visitor Overview wrong numbers of current day

Hi guys,
we have a strange behavior in visitor overview page when applying segments.
In fact: when applying a segment that supposedly should filter out a small amount of pageviews/visitors, the reports show higher number than for all visits.

Following screenshots should make it more clear:

All Visits vs Applied Segment:
e.g. filtering Operating System isnot some exotic value
→ higher number of page views and visits (what cannot be)

Strange thing:
This applies only for the current day and when segment filter only filters a small amount of data.
When date is in past, segment filters work properly. When the segment filter filters huge amount of data, is also seems to work properly - at least the results are reasonable then.

Any one else experiencing similar behavior?