Could be history building up. Bizarre, I tried deleting history and delete all history through the edit menu I tried the playback all frames to no avail. The only thing that seems to work sometimes is creating a new scene and pasting the objects in but sometimes it works sometimes it doesn't. I can get one object to properly convert and fall. But paste a few more in and that same object is now shifting in position when converted to an active rigid body and either allows me to move it properly or zips way way (usually down) out of sight if you even touch the move manipulator from one second to the next.