Index: trunk/data/validator/combinations.mapcss
===================================================================
--- trunk/data/validator/combinations.mapcss	(revision 15266)
+++ trunk/data/validator/combinations.mapcss	(revision 15267)
@@ -89,5 +89,8 @@
 }
 
-/* {0.key} without {1.tag} */
+/* {0.key} without {1.tag}, #17997 */
+*[generator:source             ][power!=generator],
+*[generator:method             ][power!=generator],
+*[generator:type               ][power!=generator],
 node[fire_hydrant:type         ][emergency!=fire_hydrant][disused:emergency!=fire_hydrant],
 node[manhole                   ][man_made!=manhole],