When your connection is ending, Toad will check to see if there is a transaction (data changed but not committed - but use of a DB Link will make cause Oracle to return TRUE for transaction if if there isn’t).
So when Oracle says yes, there is a transaction while you are ending your session in Toad, what do you want Toad to do? Automatically commit? Automatically rollback? Or ask you each time to commit or rollback(prompt)?