Came across this story via Eric Balchunas on Twitter.UBS has halted the sale of shares of the UBS ETRACS Monthly Pay 2x Leveraged Mortgage REIT ETN (MORL) until further notice. Since the announcement that it's being closed to creations, investors have bid up the shares to well above their NAV.On Friday, MORL shares hit a premium of 6% above NAV. It looks like the premium has since come way back down, which is a little surprising given that no more shares will be issued, but I'd still expect premiums in these shares going forward. MORL has been popular with dividend seekers thanks to a yield which has routinely hovered around 20%.Investors who don't want to deal with the premium may prefer the B series of this ETN (MRRL). This ETN has substantially similar characteristics to MORL, but trades right around NAV. MRRL could be much less liquid as it has just $25 million in assets compared to nearly $500 million for MORL.