Make substitute rename dummy repeated indices (when position=fixed)

Question

{a,b,c,d}::Indices(full,position=fixed).
substitute($S_{b}$, $S_{a} -> T^{b}U_{b}P_{a}$);

complains: cadabra2.ConsistencyException: Fixed index pair with two upper or two lower indices found. Is this a bug? If not, how should I proceed?

(What I'm actually trying to achieve, to understand Cadabra better, is to write the Riemann tensor in terms of the metric. Of course I do this by writing the Riemann tensor in terms of Christoffel symbols then substituting their expression in terms of the metric. In that second step I get the same ConsistencyException as my toy model above.)

Answer 1

This is an error in 2.1.2, fixed in github and the upcoming 2.1.3.