Ruta action SETFEATURE does not work with feature expressions

Ruta action SETFEATURE does not work with feature expressions:

DECLARE Annotation X (STRING s);
DECLARE X C;
DECLARE X B (C c);
DECLARE X A (B b);
W{-> CREATE(C, "s" = "c")};
W{-> CREATE(B, "c" = C, "s" = "b")};
W{-> CREATE(A, "b" = B, "s" = "a")};

A{-> SETFEATURE("s", A.b.c.s)};

Feature s of annotation matched by type A is not set to "c". This is cuased by the misinterpretation of the feature expression as a number expression, I think.