BTA moves for 2 reasons
1) They searching for better suitable location ,flow/light etc. If this is the case, it is fine except it will probly sting couple other corals while it is moving.
2) They moves because they are stressed, it can be the clown fish, ( larger size clown trying to host small BTA can do that), or it can be stress due to the new environment as well, water chemistry /flow or even slight lighting can cause this. If it starts run behind rocks, under rocks then it is because the stress that it want to hide from all the "traffic" If that is the case, you have to let it come out itself and hope it will. The more you handle it, the more it will run away.