I believe it's caused by calculating your return on the cash now if you sell, compared to the return within 10 months time if you wait till the takeover completion.
If you sell now at 66, with a 5% cash return on the bank, you have a better return that waiting 10 months for this 2.5$ increase (3.7%).... all this assuming that applicable CGT is the same now than within 10 months , which is not true for everyone as it depends on your personal situation...and ruling out a takeover bidding war... Lots of IF....
So it makes financially sense for some to sell at 66...
Hope this helps.
ALU Price at posting:
$65.86 Sentiment: None Disclosure: Held