Follow-up report to
Bug #796451 “Measure tools should support rotation constraint”
Bug #796450 “Measure tools should support snapping”
As commented in the earlier reports, the measure tool detects different intersections while dragging the measure path horizontally with 'Ctrl' pressed (or when snapping e.g. to the grid):
«measuring at 0° (…) still has randomly incorrect intersections/gaps measured (…), depending on current cursor position while dragging the mouse slightly with 'Ctrl' still pressed. Results can vary depending on measuring across sub-paths of one object or across segments of different objects.»
Tested with Inkscape 0.48+devel r11533 on OS X 10.7.4.