I have noticed all of the limited partnerships have been selling off even with good earnings!
I think there is the possibility in the new tax structure that limited partnerships may be eliminated-Canada did this a couple of years ago and those stocks sold off 30% within one year of the announcement!
In my opinion it appears that STON may indeed be the process of making a large aquisition. I believe the target of their desire is CSV. I think it will be an all stock, tax free exchange of shares and STON will thus dilute their current shareholder equity, thus the fall in price.
Disclosure: I own a large amount of CSV shares 31.5k.
Not sure of reason for fall in price, but it did allow me to pick up a couple of blocks of shares. Difficult to do, as a result of the low volume. Management just increased the dividend so I believe the dividend is safe for the remainder of the year and at 9+% tax free, it is tough not to buy more.