Sigma 18-50 f2.8 For Pentax

This is my go to portrait lens for weddings, great for group shots as there really hasn't been a situation yet where I haven't been able to get everyone in. This lens is essentially on my K10D all day long. I have had has some trouble with sharpness at wide apertures, which I think is pretty common regardless of brand. The 2.8 comes in very handy and it can focus very close to the subject when needed (almost touching the lens). The biggest piss off I have with this lens is the fact that for whatever reason, Sigma designers decided to reverse the direction you rotate the barrel to zoom in and out... why?