I tried the ILS 34R and 34L. When I did ILS 34L I was in GPS mode on the CDI. The CDI mode switched from GPS to LOC1 when I was about 1 mile from SOSIJ while still in NAV mode. I did it twice to make sure I didn’t push anything by accident and it did it both times. I don’t know about the G1000 but in real life the Collins ProLine avionics we have in our airplanes the mode doesn’t switch like that unless APPR mode is selected and then it will go from FMS to LOC on the source by itself once the LOC is captured. It could be doing a similar thing in this example. However, I did the ILS to 34R and it did not change the source at ENDEV or BOBIG. Even on 34L the waypoints stayed and they still cycled through as I passed each one.
When the GPS line changes and goes straight to the airport when you hit the transition, does the CRS on the HSI duplicate the final approach course and show any intermediate fixes such as the final approach fix? Can you take some screen shots or record it when it happens? That would help a lot.
Also, you will see some fixes on the approach plate that won’t be in the database for an ILS approach when it is selected because some of the fixes pertain to the LOC only approach and not the ILS. For the ILS you should normally see the IAF, the FAF, and the runway.