Tony, I took my first 27 deer with mechs... Though mine were by Rockets, I think the Wasp is a great head, too. The guys up above are right (especially Kodiak) about shooting the same head which may have meat matter or dried blood inside it making the blades harder to open.

All my shots with mechs just rolled the band up the shaft like you mentioned, and pulling an arrow out its entry hole will oftentimes close the blades back.