The company bought a further 594,000 shares today during the...

The company bought a further 594,000 shares today during the on-market buy back. As I was watching the screen it appeared that one block of 500,000 changed hands. I don't have broker information so I don't know whether it was Foster's that was buying, but it must have been because they couldn't have acheived 594k without this block.

My question is, "does on on-market buy back actually have to be done involving shares that appear on screens as being for sale? At no stage did the 500k of shares appear as a sell order.

If the answer is "no" then we seem to have an unbalanced market. Not everyone has the same opportunity to sell into the buy back.

I wonder whether these 500k of shares were part of the placement at $1.60 that Fosters were the underwriter for last year. Note that it is Fosters who are conducting the first part of the buy back.