Xandrax

In regards to the higher level thief outside Riverwood, this bug also causes a Bandit Marauder to spawn at the tower near Bleak Falls Barrow, I believe it may be linked to Undeath, as that's the only mod I had that you had as well. After disabling Undeath, the Thief was gone, as was the Bandit Marauder. From what I've read, the Thieves Guild Brynjolf bug is linked to this.