Checkboxes that expand into another set of options, as opposed to headers that expand a set of options, are supposed to be indented a bit. The idea is to give a visual hint that this is related to the checkbox. That effect is obvious under a normal header.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.