A buddy and I were testing this earlier. He was watching the TADS from the back while I searched for targets in the CPG seat. Whenever I would activate LMC mode, the TADS crosshair would move from his POV. Sometimes just a few feet off the target, sometimes by several dozen meters. Seems to be hit or miss when it desyncs, as not 20 minutes before I was using LMC and bumping the MAN TRK stick to move the crosshair with a squad of infantry and it was hitting right on target (same helo, same sortie).
Another person in our group pointed us to a list of things to do as a workaround (cycle safe/armed from the pilot's seat, cycle NAV/ATK mode on TSD, change laser codes, switch ACQ source, etc.). Only thing that seems to fix it for us is to keep jumping into a new bird until it works...even then it may work for the first couple of shots or it may work for the duration of the sortie....or not at all.