Sorry it took so long. The rSAP connection is running fine and then suddenly aborts. At the same time the phonebook transfer is active, so it may be that the phonebook causes the car to shut down the Bluetooth connection. This happens sometimes with older HTC stock ROMs. They even may crash the car headunit.
Try to delete all unused data from the contacts, first of all pictures. I don't think you can exchange Bluetooth.apk with a HTC stock ROM, so this will not help. The last possibility is to install a custom ROM based on AOSP/CyanogenMod.