FINAL UPDATE: I ran into the same problem with other instruments as had been the case with Retrologue: HALion Sonic started to exhibit the same “auto-adjust” problems without notice. The culprit in all cases was the driver for the Alesis QX49 controller.
Once I disconnected the QX49’s USB connection and ran the keyboard through another MIDI controller, the problems with all the instruments magically went away.
If you happen to have one of these Alesis controllers, ignore the driver and use something else. You’ll pull less hair out of your head (a big plus when you have as little as I have left … heh heh).