I play in a large resolution (1440x768) which is also widescreen. While in clockwork floors where dust is around the player (see screenshots 1 & 2) the radius of the dust effect doesn't reach the edge of the screen (screenshot 3)
http://i.imgur.com/kkJhO.jpg - dust effect as seen in clockwork
http://i.imgur.com/x4Wx1.jpg- a floor without the dust effect
http://i.imgur.com/a8nsD.jpg - where the dust effect ends
I play in 5960x1080 and can't seem to find the problem you're having. It might be limited to just your computer. If you like, I can test on mine to see if it does have the same bug as yours.