Consider the following scenario in System Center Configuration Manager 2007 Service Pack 1 (SP1):
In this scenario, the changes are not updated on the BDP. This problem occurs randomly.
If you're experiencing this issue there's a new hotfix available to address it. See the link below for details:
KB973762 - A package that is several gigabytes is not updated on a branch distribution point (BDP) in System Center Configuration Manager 2007 Service Pack 1
J.C. Hornbeck | System Center Knowledge Engineer