HP Tech Support confirmed to me that a small change has been made in the hardware to fix a rather obscure problem, and the first few hundred units that were produced are being replaced with the updated model. This will mean a week or two delay before some retailers will have stock.
It's nice to know that HP cares so much about the quality of the device that they are willing to do this.
If you have one of the original units, you can get it replaced through the vendor where you purchased it. If you buy an OmniGo from this date forward, you will receive the updated model.
If you don't want the replacement, you can avoid any problems by following this procedure:
1. When replacing the main batteries, before you remove the old ones, run the Setup app and turn OFF the feature "Touch Screen to turn on"
2. Double check. There should be no X in the box next to "Touch Screen to turn on"
3. Now you can turn off the unit by pressing the on/off key and remove and replace the batteries normally.
That's it.
Steve