Piyush and Erik,
Good query and observations from your end.
What you see in the md04 screen needs to be drilled down by another level to see further details.
For any requirement system creates the schedule lines and if you look at EKET table you would see that in addition to the item number seen in md04 there is another field ETENR called schedule line number.
so for multiple requirements even if ithey are on the same day, you should see that the system creates multiple records .
Can you check the EKET table and confirm your observation? Agree or Disagree?
Again FYI schedule lines are meant to serve the purpose of an 'individual' nature and requirement and hence the design like that in SAP.