Locking shop signs of other players

Minecraft Username:
314

Brief Description:
It is possible to prevent the owner of a shop sign from deleting it by locking it.

Instructions:
1. Player A creates a sign.
2. Player B locks it with /cprivate or /lock.
3. Player A can't remove the sign until player B removes the lock.

How many times did you recreate this bug?:
Once, but it seems like a bug in the plugin itself and so it might always happen.

Result:
Player A can't remove his sign until player B removes the lock. This could cause problems with money signs
or shops in general.

Expected Result:
Being able to remove a sign you created.

Evidence:
I tried it with @jassimq as witness/helper.