what does this mean "Market speculation has bet that head stock...

what does this mean "Market speculation has bet that head stock Centro Properties Group would be folded into listed sister trust Centro Retail. There were a number of options including "stapling" the units in the two trusts together, he said."

Blackstone gets the assets but the securities remain with the shareholders. What bargaining power do the shareholders have to get them stapled to CER?
(Am assuming that stapling them means a share in ownership).