Ann: Becoming a substantial holder, page-6

It means the stock has been borrowed by UBS and not lent out. The lending out creates the reduction in interest of UBS.

THeir interest can go up by borrowing or by the shares being returned to them by the borrower.

(This is seperate to actions by related parties e.g. UBS asset management which is operating independently as a regular fund manager but due to the relationship it all needs to be aggregated)