This bug should be easy to replicate:
a)Make some asteroid miners, put them in a TG, and move them to an asteroid. Call the TG "Mining 1" or whatever.
b)Make some more, move them to a different asteroid. Call this "Mining 2".
c)You should see each asteroid reporting the correct number of orbital mining units.
d)Give Mining 2 order to "Join" Mining 1.
e)When it's done, you'll see Mining 1 has all the ships in it from Mining 2 and Mining 1, as you'd expect. However, the "Orbital Mining Modules" on the Mining tab for that asteroid will not have changed (at least, it didn't for me).
f)Give Mining 1 orders to move to anywhere, preferably somewhere far. Advance the clock a few days.
g)Cancel those orders, have the group move back to its original asteroid.
h)The mining tab will now show the correct number of mining units.
It seems as if the program checks a task group's total mining units only when it first arrives at the asteroid; it doesn't check if the task group's composition changes. (While I didn't test it, this could lead to an exploit; move 10 mining ships to an asteroid, wait a few days, then detach all but one; lather, rinse, repeat. If I'm correct about what's happening, you'll get the full mining benefit of a lot more ships than are actually orbiting.)
