I did not see this particular issue before, but I've noticed other weird issues.
Like you can not delete the layer Defpoints from the dialog nor with Purge, but you can delete it with the command LAYDEL.
Also I've seen drawings without layer "0", though every action will cause a Fatal Error.
A previous version of Microstation saved unnamed blocks with a "#" instead of a "*", which was still accepted by AutoCAD except purging.