I am thinking it is just through dilution of their holding by...

I am thinking it is just through dilution of their holding by the issue of additional shares.

The announcement says they ceased being a substantial holder on 27th April -the day NSL relisted and there is no way 13M shares traded that day. So I think it is just that they relisted with a greater number of shares on issue.

Also if you look at the top 20 shareholders disclosed by NSL in their announceets riorto relisting it has the 'CBA' holding as 4.94% of the company which is less than the 5% that would qualify them as a substantial holder.

Just my best guess though.