I had the exact same issue with my H16 except when my base pulled out, it ripped out the aluminum on the bottom of each rivet and my mast hit the ground, hard. I just epoxied the base back in and it's worked fine all season so far. I think the new hobie 16s aren't even riveted at the mast base, they are only epoxied. Now, when I'm stepping the mast, I keep one hand low on the mast pulling it back so the step assembly doesn't swing up.
jrg