The Vegas program burns a Blu-Ray Format disk, not an avchd disk.
I thought the Panasonic unit has a usb port for media, you should be able to make your own custom template and render the video as a xxxx.m2ts video file.
As a test on the usb port for media you may have to play around with the file extensions that the pana recognizes.
The vegas program will work if you burnt to a blu-ray disk.