They are taking a position. As you said they have been quietly accumulating for months now. Puts them just short of a top 5 holder.
I suppose they may be holding for the dividend, perhaps expecting a tax ruling that will be favourable to them, but they must see something there they like - though of course 5% of AOH is chump change for MS, so perhaps it's just a mug punt.
It will be interesting to see where they stop.
AOH Price at posting:
23.5¢ Sentiment: Buy Disclosure: Held