Breaths & Pauses accumulate offset
Changing the X-offset of a breath mark or similar item to a nonzero value causes the offset to accumulate with every layout "redrawing" update. The result is a rapidly growing and score-breaking space around the mark, forcing you to delete it and not use any offset. Almost anything triggers this accumulation, from toggling visibility of an element to placing notes to using the undo command. If you really want to see it take off, just drag a notehead around.
To reproduce this behavior:
1) Open or create a score
2) Place a breath mark, caesura, or other item from Breaths & Pauses menu
3) Change the X-offset, either by typing a new value in the inspector or dragging the element
4) Modify the layout, e.g. by placing new elements or changing properties of existing elements
With each action the actual offset is increased by the amount currently typed into the X-offset field.