Noticed this today in both Buying Time and Dragon's Hoard.
After buying 5 more Kobolds and putting down my initial line of torches, I proceed to reconnoitre the vicinity to clear out mobs in areas with purple crystals. However I now noticed I was being followed by 6 or 7 empty handed kobolds who would proceed to pick up crystals in the area I just entered even without torches being there. This would continue if I went back into the vicinity of empty handed Kobolds, including during the fight with the Marilith where about 8 kobolds followed me as I pulled her away from the centre and then proceeded to die to her AOE melee.

Anyone else notice this?