  Kra\'skiewicz and Pragacz introduced representations of the upper-triangular
Lie algebras whose characters are Schubert polynomials. In a previous work the
author studied the structure of Kra\'skiewicz-Pragacz modules using the theory
of highest weight categories. From the results there, in particular we obtain a
certain highest weight category whose standard modules are KP modules. In this
paper we show that this highest weight category is self Ringel-dual: this leads
to an interesting symmetry relation on Ext groups between KP modules. We also
show that the tensor product operation on b-modules is compatible with Ringel
duality functor.
