Comment 3 for bug 277958

It appears that the cloned text cannot have a custom stroke style when the inner <tspan> element of the original text object has its own style definition that includes stroke and stroke-width.

To fix it:
1) select the original text object
2) switch to the Text tool
3) select all text (Ctrl+A)
4) 'Unset' the stroke for the *selected* text

result: the stroke of the clone now is rendered as expected.