Actually, at most times shorting the preferred and longing the common is a good safe arbitrage. The preferred converts into 2 shares of common, so a short of one share of preferred is against the box of the 2 shares of common long.
Right now the preferred is $31 and converts to 2 shares of common, currently $7.27 per share. Buy 2 shares for $15, sell a share of preferred for $31 and collect a net of $16. There are 4 remaining dividends before conversion into common (March 2014). So you pay $5.5 out in dividends.
It is free money, just sitting there. Of course there is some risk ... the preferred might be recalled at an inopportune time, the interest for borrowing the preferred shares might jump, etc. But the fact is that the preferred is overvalued, most likely as some investors chase yields without noticing the expiration of the dividend and conversion.
But if you can borrow preferred shares, go for it. The arbitrage trade is large right now.