Hi, I had the same problem. I found a work around on the Microsoft Forum from " Wilco 3563"
This is a limitation of the current development model of the G1000 NXi from working title. The Multipanel should work fine with any aircraft not using the G1000. You can enter the altitude from the panel in the sim and it will work OK except for displaying the 99000. If you want to go back to the stock G1000 until they work this out, you can delete the NXi from the content manager.
I deleted the G1000 NXi from the content manager and I no longer have the problem.
Hope this helps you,
Steve