Okay, I bit the bullet and used the Windows Device Recovery Tool to leave the Insider FR. As soon as it connected to my Elite X3, it showed that firmware 0002.0000.0026.0118 was available. To install the firmware I needed to get the phone into a "ready" state by rebooting and holding the "up" volume button until the phone went into the flash ready state. After all was said and done, I was out of the Insider FR and back at 14393. Connection to / Disconnecting from the Desk Dock was finally working like it should. I used it over the weekend this way, before attempting to get back on the Insider FR. Now back at RS2 Build 15055. Had a couple of hick-ups with the Desk Dock not working right with my display / mouse/ keyboard, but it seems okay now. Unplugged the power from the Desk Dock seemed to help. Now my work setup of the Desk Dock with a Acer 19" display (connect via DVI to HDMI adapter to the Desk Dock), and a Lenovo ful-sizedl wired keyboard and HP wired mouse (both connected via USB to the Desk Dock) is working as I envisioned. Still not sure if it was the latest Insider builds causing the problems, or the older HP Elite X3 firmware.
The setup ran fine on the older Insider builds right after I got the phone at Christmas. It wasn't until the end of January that the phone display wouldn't come on after disconnecting (I believe the phone was still working, since my Bluetooth connection was still active), and I was having problems with the display coming on / connecting when I plugged my phone into the Desk Dock. In addition, there were numerous phone resets/reboots while connected to the Desk Dock. We'll see how thing go from here. But all-in-all it's working MUCH better now. Have to expect some problems while on the Insider builds!