libbluray tries to access not yet mounted disc

On macOS, libbluray unmounts the disc for low level access with libudfread, iirc. Then it re-mounts it but tries immediately to read from it, which will fail as the disc is not yet mounted. I haven't yet found any API to wait till the disc is mounted again though, so not sure what the best solution for this might be.

For what exactly does libbluray has to unmount the disc in first place?