It's a myth - Gaps aren't always filledLook at the chart for GBR. Some of the gaps have been filled, some never will be. There are actually thousands of examples of gaps never being filled of being filled decades after they form only because stocks swing up and down or eventually retrace to zero as they head to bankruptcy.
Maybe the gap on ZENA will be filled because there are too many shares out and there's too much competition in the POT market - but maybe not. We'll see.