Ann: Change in substantial holding from PCG, page-14

Likely to be the usual late in financial year realisation of a tax loss by selling to an associated party (better to make the loss this financial year to offset other income or gains elsewhere this financial year - and thereby defer tax to next financial year; and then when the BLK share price goes up in the next 12 months, then find more tax losses elsewhere before 30 June 2018).
If I'm wrong, then we'll know pretty soon who the new BLK substantial shareholder is.
How exciting!