Subselect sets values in wrong element

Given

<foo>
</foo>
<foo>
<bar />
</foo>

and having a subselect for the first "foo", when the subselect returns "bar=X", this will result in

<foo>
</foo>
<foo>
<bar>X</bar>
</foo>

but it should be

<foo>
<bar>X</bar>
</foo>
<foo>
<bar />
</foo>