Infinite gold farm bug?

Potentially just needs clarification, but I noticed with unstable breaches in mirages that as long as you don't kill the boss/rare mobs after stabilizing the breach, you can continue to get the gold balls from the mirage wish (the 4% chance on kill) off the breach mobs which spawn indefinitely.

The breach doesn't seem to close either, but I'd only noticed one open for 5 minutes because I was struggling to kill a proximity+wither/chaos resistant mob as a poison build. Can GGG please confirm if this is some kind of intended gold strat, if I'm missing something, or is this an exploit?