Assigned(h) and left(h) are not changed after the meeting length is changed

I'm not sure if this is an issue or a feature, but in my case it seems like an issue. The following is applicable for V5.0.5:
I create a meeting with let's say a length of 1 hour. After that I add attendees and they receive automatically Assigned(h): 1 and Left(h): 1.
If I then adjust the length of the meeting (make it 2 hours), the field Assigned(h) and Left(h) of attendees remains with original 1h, whil I need it to become 2h. The only way to adjust the is to remove the attendees and add them again.
Is this a normal behaviour?