Its not even in playback it just shifts automatically when I make it into a rigid body and then completely disappears when I try to move it without hitting the playback button. Strangely though it only seems to happen to objects I've been altering for awhile. A freshly created cube doesn't seem to have the same problems.
Make sure your playback speed is set to "Play every frame" in your animation preferences.
Could be history building up.
nope, I even ungrouped to be sure. Strangely converting to physX dynamic rigid bodies or ncloth gives me none of the issues that the default active rigid bodies do.
Make sure it is not intersecting with any other geometry, as this can cause issues.