Also, when Luffy squeezed some shadows out of him earlier, Moria merely turned them into shadow bats which then attacked luffy. So, it seems that if he retains enough mental stamina to keep them under control
Good observation, bogia. I think Moria could still maintain enough control over the thrown up shadows to keep the from going back to their original bodies. They seem to be just rising into the sky on the last page, whereas Nightmare Luffy's shadows flew away in every direction, going right back to their masters.
Why would he need to order them when they are free? Brooks shadow returned after Zoro beat up Ryuuma.
The difference is that Ryuuma was completely purified at the time, so Moria holds no control over that shadow at that point, so of course it'd go straight back to Brooke, same applies to Tararan.
Obviously Moria isn't purified, he could still have a certain degree of control over the shadows, so I don't think the same rules apply to him. (I think I've said this before)