The Globe and Mail reports in its Wednesday edition that Pershing Square Capital Management head Bill Ackman has ended his love affair with Canadian Pacific Railway. The Globe's David Parkinson writes that now it is up to other investors to decide if they need to break it off, too. Mr. Ackman announced Monday Pershing would sell up to seven million shares of CP in the open market over then next six to 12 months. Pershing's sale would trim its stake back to less than 10 per cent, from 14 per cent. Investors want to know what Mr. Ackman's decision implies about the company and their investment in it. Mr. Ackman said nothing against CP, but its share-price success had swelled it to 26 per cent of Pershing's holdings, which is too much concentrated in a single stock. Mr. Parkinson says trimming the CP position is just good portfolio management. If Pershing sold the seven million shares today, it would get nearly $1-billion, which is triple what it paid for them in the fall of 2011. With the price expensive and the big gains from CP's restructuring already largely priced into the stock, Mr. Ackman may be cashing out near the top. Finally, Mr. Ackman may now have doubts Keystone will fail.