IFD 5 Series & IFD 4 Series Touch Screen GPS/NAV/COM - Final leg cleared when approach selected

if the procedure airport is not the IFD active waypoint when an approach procedure to that airport is selected, the IFD effectively moves the procedure airport to its appropriate place in the selected approach procedure creating a gap between the waypoint prior to the procedure airport and the first fix for the approach.

This is the scenario you described. After this occurs and if desirable, the procedure airport can be added as a waypoint prior to the gap that was created by selecting the approach procedure.
If the procedure airport is the IFD active waypoint when the approach procedure to that airport is selected, then procedure airport remains the IFD active waypoint and a second instance of the procedure airport occurs at the appropriate place in the selected approach procedure.

Had you waited until after GOBBY to select the RNAV 17L approach, this would have been the scenario you would have been in.

FWIW - the "Activate Approach" LSK (only available if the active IFD waypoint is followed by a gap before an approach) also has different behaviors depending on the situation:

If a VTF approach is selected, The Activate Approach LSK performs the same operation as the Activate VTF LSK or selecting the FAF and using the Activate Leg LSK.
If a non-VTF approach is selected and the IFD active waypoint is the procedure airport, selecting Activate Approach LSK performs the same operation as performing a direct-to the IAF from you present position.
If a non-VTF approach is selected and the IFD active waypoint is not the procedure airport, selecting the Activate Approach LSK eliminates the gap by connecting the active waypoint and the IAF.