Robert,
All my eqpt is the same rev of the DCS software. I have upgraded my 3 TIUs and 4 remotes and then backgraded them, and then reupgraded them, all with no difference.
That would point to a defective remote key or a layout DCS signal issue.
Now, don't run out and buy a Rev. L TIU, just because there's good chance that it would correct your problem. You just stick with your "tried and true" antique TIUs!