I can't document this, but my understanding is that buybacks need to follow the following rules:

• no more than 15% (or is it 20% or 25%) of the daily volume
• buys must be at the bid (ie bid support, can't hit the ask)
• no buys during first or last 30 minutes of trading

I look forward to the buyback since the share price didn't have legs to sustain it's last run. Maybe this time it will maintain a more bullish trading pattern.