This is not a bug, merely an observation. Using Slic3r 0.8.4, concentric fill pattern for solid layers. The object is a circular disc with 5 holes equally spaced near the outer radius. When I orient the object with a hole oriented towards y-max, I get a very nice, symmetrical fill pattern. However, if I orient the disc with one hole oriented towards y-min, I get a really weird fill pattern- sort of off-set and distorted. I am not sure if this "feature" was also available in earlier versions, and I have not tried yet rotating the pattern with the key hole oriented along the x axis. But I am rather surprised that the fill patterns would vary so significantly depending on the orientation of the object...
