22382: Fixes possible bad union of features (#380)

howso/react_discriminative.amlg

@@ -129,7 +129,7 @@
 						)
 
 						;maintain order of context features to be as specified
-						(assign (assoc context_features (union context_features preserve_feature_values) ))
+						(assign (assoc context_features (values (append context_features preserve_feature_values) (true)) ))
 						(assign (assoc context_values (unzip context_values_map context_features) ))
 					)
 				)