From the Ubuntu bug report:

I found this report a little difficult to understand, so here's my
interpretation of it after some experimentation (reproducing the bug in the
process). I hope this is accurate.

Create new document, then Tools -> Options -> OpenOffice.org Writer -> Grid; set
Snap to grid, Visible grid, resolution to 1cm for both, subdivision to 1cm for
both. Enable the Drawing toolbar in View -> Toolbars, then place a rectangle
somewhere. Observe that Writer shows you the outline of the rectangle as it's
drawing it, and then when you let go of the mouse button it actually places it
one subdivision further down from where it said it was going to. Next (zoom in
to 200% to see this) if you try to move the rectangle it doesn't snap properly
to the grid, but snaps to something slightly offset from it.

This smacks of a rounding bug, perhaps.