I had a similar experience with another stock I own, when they...

I had a similar experience with another stock I own, when they were admitted into the ASX300.

There was heavy buying as a result of Instos having to buy the stock (some Instos have to buy a certain percentage of every stock in whatever index it plays in).

So in my other stock, there was a passive type Insto/EFT fund who had to buy into the stock, and had to buy enough shares, such that it made approx 5% of the Insto's overall share portfolio. This created large volume and SP increase.

The risk with this is of course is, if the stock falls back out of the Index, then the Insto may be forced to sell back out again!