Yeah, the bonus disc AR was deprecated when NGS was released in may last year. All "bonus discs" like this should be converted into 2-disc releases - but unfortunately this could not automatically be done by the system in the conversion, so there are lots of such release groups to tidy up.
Some have become completely screwed up with the ARs pointing everywhere because the system could not working out which bonus disc corresponded to which "release event" from the original pre-NGS release. This makes it quite hard to work out unfortunately.
The easiest way to fix them is to look at where the AR is pointing and try and find the correct "first disc" release based on catalog numbers, barcodes etc; then to either
A) If the first disc is available on its own, and there is no existing "disc 1" release for that bonus disc
1) edit the (bonus disc) release
2) remove (bonus disc) from the title
3) check release events/data/cat numbers. Sometimes a bonus disc has a separate cat # to the first disc, and so both cat#s could be included
4) on the tracklist tab, add a new dis
5) base this new disc on the existing tracklist from the release where the AR is pointing to
6) re-order the discs
7) check whether the bonus disc needs a disc title
8) enter edit release/add medium edit
9) enter another edit to remove the bonus disc AR
B) if there is an existing "disc 1" uniquely corresponding to the bonus disc
Merge the two releases together, appending the bonus disc to the first. You might need to clean up the cats/barcodes after merge as well.
You also might find it useful to try and use discogs links and such to confirm the first disc's tracklist.