After engaging in combat with the Dungeoner’s and Raider’s Tanking dummy, I am unable to leave combat. I believe this is due to the training dummy being marked as my adversary due to Dauntless Duelist. This only occurs on the aggressive training dummies (tanking dummies). Dauntless Duelist seems to clear on the regular dummies after line of sighting them.
The only way I was able to get out of combat with those dummies was to portal to Oribos (I have the rank 3 portal in my Sanctum). I tested this on aggressive NPC’s and I was able to clear Dauntless Duelist by running far enough away, it just seems like something with clearing it on “unkillable” mobs like dummies.