The profiles option to "Postpone background programs and maintenance tasks" will re-check itself if you return to any of the 3 profile Configuration dialogue boxes. The feature is not actually turned back on unless you click "Save" without unchecking it, but will always appear to be on if you look at the Configuration window.
This happens on both my Windows 7 64bit desktop and Vista 32 bit laptop.
To recreate this issue
Open the BitDefender interface
Go to Tools > Profiles
Click "Configure" next to any of the 3 profiles
Uncheck Postpone background programs and maintenance tasks
Click "Save"
Close the BitDefender interface
Re-open the interface and return to the previous Configure dialogue. The Postpone background programs option will be re-checked.