You don't say what the mountpoint is for the filesystems on your encrypted LVM partition; but evidently they aren't any of the standard mountpoints that are considered blockers for starting lightdm.
The behavior in this case is expected - this is not a bug but a misconfiguration. If you want launching lightdm to wait until these filesystems are decrypted, you will need to mark those filesystems 'bootwait' in /etc/fstab.
You don't say what the mountpoint is for the filesystems on your encrypted LVM partition; but evidently they aren't any of the standard mountpoints that are considered blockers for starting lightdm.
The behavior in this case is expected - this is not a bug but a misconfiguration. If you want launching lightdm to wait until these filesystems are decrypted, you will need to mark those filesystems 'bootwait' in /etc/fstab.