I have a theory,
that it was cut from cloth used for more than just flags. If they print union jack patterned fabric for general use, with a repeating pattern that has the diagonals always meeting where verticals and horizontals cross, then you'd also have verticals and horizontals crossing without diagonals meeting, despite there being no such part of a union jack.
( ,
Tue 12 Nov 2013, 20:26,
archived)