A couple of observations - do I have this right?

the interesting thing is that it seems to me that once a remote is tethered to one TIU, the remote stops talking to the other TIUs, is that correct?

 

also, it seems like any untethered remote can't talk to the TIU that has a tethered remote. Is that correct?

That's correct.

From page 114 of The DCS O Gauge Companion 2nd Edition:

• When operating in Super TIU mode, if a DCS Remote is connected (tethered) to a particular TIU by connecting the DCS Remote's Programming (TIU Connection) port to the TIU's Remote Input port, that DCS Remote will only be able to communicate with engines that are present on tracks connected to that TIU's channels, regardless of whether or not Super TIU mode is in effect 

• Tethering a DCS Remote to a TIU restricts communication between those two devices only to each other. No other DCS Remotes or TIUs can communicate with a DCS Remote or TIU that's tethered

This and a whole lot more is all in MTH’s “The DCS O Gauge Companion 2nd Edition", available for purchase as an eBook or a printed book at MTH's web store!

The more engines you have getting track power (they don't have to be powered up) the longer it takes to load them into the remote. And if more than 5 or 6 they may not load right.

The remote will only communicate with the TIU it is tethered to.

I've never seen a Z-4000 do what you have experienced with yours. Does the red light blink when it does it?

Thanks Barry. I didn't recall reading that in the book. I read it honest. 

No Joe, it doesn't. Bothers me. 

Well, if the red light isn't flashing or on, I would say it isn't shorting out. Check the voltage with a volt meter when it shows 2.4 volts. It just might be an incorrect reading of the transformer readout.

I've never seen a point readout on the volt meter of the Z-4000 once throttled up. It's usually whole numbers that show. Now the amp meter does readout the amps such as 2.4