GriefPrevention is powered by permissions. Every action done in a world is checked against a specific flag permission. If you are trying to figure out what is causing an action to be blocked or not to be blocked then /gpdebug is what you will need to use.
To record all flag permission checks, enter
To record all flag permission checks for a specific user, enter
/gpdebug record username
When done performing actions to record, enter
This will generate a link which you simply double click to see output.
An example of output shown is