In and Kraśkiewicz and Pragacz introduced representations of the upper-triangular Lie algebra class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0021869316302332&_mathId=si1.gif&_user=111111111&_pii=S0021869316302332&_rdoc=1&_issn=00218693&md5=d5fa10ac0221d8d55dc37b02250cf57d" title="Click to view the MathML source">bclass="mathContainer hidden">class="mathCode"> whose characters are Schubert polynomials. In [12] the author studied the properties of Kraśkiewicz–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 class="mathmlsrc">class="formulatext stixSupport mathImg" data-mathURL="/science?_ob=MathURL&_method=retrieve&_eid=1-s2.0-S0021869316302332&_mathId=si1.gif&_user=111111111&_pii=S0021869316302332&_rdoc=1&_issn=00218693&md5=d5fa10ac0221d8d55dc37b02250cf57d" title="Click to view the MathML source">bclass="mathContainer hidden">class="mathCode">-modules is compatible with Ringel duality functor.