[Brian]

Brad, it sounds like you're encountering a combination of the issues discussed in the thread. The shape is 50 by 50, but the stroke is centered on the border of the shape. The 1-pixel stroke is a half-pixel inside and a half-pixel outside the border of the shape. OmniGraffle then does sub-pixel blending to produce what you see on screen. Those blended pixels are going to to make your stroked shape slightly larger.

Since you have "current selection" selected as your export type, OmniGraffle defers to that sub-pixel blending and exports the extra pixels. If you size the canvas at 50*50 and switch to the "Current Canvas" export type, OmniGraffle will instead clip the shape at the canvas borders and omit the extra pixels. Does that help?