How to stop baobab from scanning schroot mounted dirs.

Baobab scans the filesystems mounted by schroot (parts of the top level filesystem that are binded inside the chroot) without noticing that they are already scanned as part of the root filesystem. This makes baobab report inaccurately about the used space on the disk. These filesystems do not appear in the preferences dialog box. Is there a way to exclude them from the scan?