First at the end of class, wrong initalization.

-    private UIntType _x = m ? a + c : (a + c) % m;
+    private UIntType _x = m ? (a + c) % m : (a + c);
 };



Second in this method we can assome that if m is 0, and type is int, it was really 2^^32 (0 in int).

     private static bool properLinearCongruentialParameters(ulong m,
             ulong a, ulong c) {
+        static if (is(UIntType == uint)) {
+            if (m == 0) m = (1uL << 32);
+        }
         // Bounds checking
         if (m == 0 || a == 0 || a >= m || c >= m) return false;
         // c and m are relatively prime

This problems are orthogonal to the my proposed optimalisations in bug3738.