It might be as simple as the AMEX listing under the new shorting rules that came into effect Feb 28th. gold888888 posted the following on the ECU board:

"I agree with Pic that GPL has been "liberated" because they trade on the AMEX. Yesterday, 02/28/2011 all stocks on AMEX, NYSE and NASDAQ saw limits to shorting imposed by our "vigilent" regulatory agencies. This only shows you how many shares were shorted (naked ?) for GPL and how many shorts have run for cover. GPL has thrown off it's yoke and now runs free. Can you imagine how many shorts would run for cover if the same thing happened to ECU ????"