The other interesting omission from the report is the tracking of the other aircraft. The report says that there were 5 aircraft conducting approaches to Hotham at about the same time. It does not say if any others flew missed approaches, or if they all flew the approach without difficulty and landed first time from the approach. The pilot of VH-OWN was without question a competent pilot with more experience on King Air's than most. If VH-OWN was the only aircraft with tracking / missed approach difficulties, then it would add credence to the pilots claim that there were GPS / autopilot faults.
VH-OWN had a C129a Garmin GPS 155XL (which at the time was completely legal for IFR). The report comments that the other 4 aircraft did not have the same tracking difficulty as VH-OWN but is deficient in not considering the GPS installations of the other 4 aircraft. If (for instance) they all had C146a GPS recievers (eg Garmin GNC430, Garmin GNX650, Garmin GNX 750, Garmin GNS480), then this would be a very significant fact that would deserve further investigation.
Also, the pilot of VH-OWN was criticised for not following the published missed approach. However, when I first flew into Hotham I had a charter pilot in the right seat who had very significant experience flying into Hotham. When we flew in VFR he pointed out to me that the published left turn missed approach was over rising mountainous forest. Whereas a right turn was over descending grassed terrain that led into a valley. His comment was that the right turn was a safer missed approach route that the published one and that it was frequently better to take the right turn and descend or remain at altitude under cloud, then climb into cloud over rising hostile terrain. It would be interesting to know if the pilot of VH-OWN was doing this. I guarantee that if I had any concerns about the operation of the GPS or autopilot, I'd turn right and remain visual until my thoughts were collected rather than turning left and immediately climb into cloud over rising "tiger country".