I have an Extang Tuff Tonno and it latches the same way. I usually take mine off in the winter because it's almost impossible to latch down when the vinyl is cold.mine stays completely still at any speed. the bar rotates back and latches by the tailgate and pulls the cover tight
http://www.stylintrucks.com/parts/extang_tuff_tonno_tonneau_cover/1960.aspx?attributes=1104000028_4294855392_4294855385