Ann: Daily share buy-back notice - Appendix 3E, page-9

Listing Rule 7.33 states "A company may only buy back shares under an on-market buyback at a price which is not more than 5% above the average of the market price for securities in that class. The average is calculated over the last 5 days on which sales in the shares were recorded before the day on which the purchase under the buyback was made."

As such, company undertaking a share buy back is not allowed to artifically inflate prices.
It would also be pretty obvious if they were stepping in to prop prices up, by the volume of shares purchased as the share price fell.

Seems to me that they are allowing the price to go with the market, and are merely taking a few each day. If they take less now, it leaves their powder dry to take more later.