Which is why it was supposed to then scrap those and move to layer 5, 6, 7 etc. but it didn't.
Nope...it only does that if you tell it to with the clear award thingy...basically the computer will go through the layers and find pairings that meet your preferences. When it has enough to make a legal (80 or 75 hour) line, it'll go through the layers again with line properties and try to arrange those pairings it got when it went through the first time. If it can't do anything based on your preferences, it'll just do what it wants....If you want it to go on to layers 5,6, and 7, you have to use the clear award function. If you restrict it (with 15 days off in your case), and it can't figure anything out by layer 7, everything else is dropped, and you get 9 days off.
If you want some tips on bidding, PM me and I'll help you out. I bid under PBS for a year with varying seniority, and was never surprised by what I got. All you have to do is properly pimp the system....