For most people the front of your hair (crown to forehead) grows slower than the back (crown to kitchen). Reaching Apl will happen in the back first and the hairs will not be APL at the same time. The hair tends to grow fastest at this time.
NOw once you get to about BSL or BSB this this is when the hair growth will take longer to get to waist length. At this stage, many of the shorter hairs will be playing catch-up and the longer hairs will appear thinner. Once you get past this stage the longer hairs will towards waist length. This process may happen again in reaching hiplenght, if that is your goal.
If you dont like the way it looks you can dust or light the hemline should not look too bad. Just keep in mind to try to do these dustings yourself, because most stylists will take off more than you woul like
Chicoro has a great explanation on her blog:
http://members.fotki.com/Chicoro123/