I don't know if it's primitive mobs fault or extra utilities fault, but when you capture a lost miner with a golden lasso in the surface he drops emeralds, and when you release and recapture him, he still drops emerald, it's a really bad thing and it opens the door for cheating emeralds.
I tried posting the issue to extra utilities author but I can't find a way to contact him.

This is likely because there were some saving issues with the Lost Miner. Could you check if its fixed in the 1.2 alpha if you have time? Thanks!

And sorry for the late response

It's still the same in 1.2 alpha, but I doubt it's primitive mobs fault cause when I tried the imprisonment tool from Industrial forgoing, it was working just fine.

the 1.2 update is awesome though, I love it

You can fix this by making the miner to check for the condition and reward you himself, instead of you right-click to receive the emeralds

This one is inside a village, have access to sky, yet is still "lost"
https://imgur.com/syphF9g

I can make it so you need empty hands to do it; that should fix it as well.
Actually I just did for the next version.

Carry On mod issue incoming

that should resolve the issue, thanks man :)

This has been added in 1.2.1, please also update MultiMob for that version :)