sortheader() with duplicate column names overlays values

[bmaggard]

import petl as etl

t1 = etl.wrap([
    ['id', 'foo', 'bar', 'baz'],
    ['a', 1, 2, 3],
    ['b', 4, 5, 6]])

t1.sortheader()

bar	baz	foo	id
2	3	1	a
5	6	4	b

t2 = etl.wrap([
    ['id', 'foo', 'foo', 'foo'],
    ['a', 1, 2, 3],
    ['b', 4, 5, 6]])

t2.sortheader()

foo	foo	foo	id
1	1	1	a
4	4	4	b

[alimanfoo]

Thanks @bmaggard, it would be good if possible to fix this so that sorting of columns with the same name is stable and doesn't overwrite data.