Good question Kansai.
I have looked through the capital raising documents setting out the restructured deferred consideration payments and, while they are clear about no dividends being payable, there is no reference to buybacks. I am guessing the issue was not contemplated because Photon was so debt ridden at the time. A buyback after the final Tranche 1 deferred cash payment in september 2012 would be a great result.
