Use the layer's projection.

In setMap, the layer gets the map's projection if it doesn't have its own. And since a layer can have a different SRS code than the map (but a compatible one, i.e. with OpenLayers.Projection.transforms[mapProj][layerProj] being OpenLayer.Projection.nullTransform), the axis order can be different.

lib/OpenLayers/Layer/WMS.js

@@ -175,7 +175,7 @@ OpenLayers.Layer.WMS = OpenLayers.Class(OpenLayers.Layer.Grid, {
      * {Boolean} true if the axis order is reversed, false otherwise.
      */
     reverseAxisOrder: function() {
-        var projCode = this.map.getProjectionObject().getCode();
+        var projCode = this.projection.getCode();
         return parseFloat(this.params.VERSION) >= 1.3 && 
             !!(this.yx[projCode] || OpenLayers.Projection.defaults[projCode].yx);
     },

tests/Control/WMSGetFeatureInfo.html

@@ -290,19 +290,19 @@
     function test_mixedParams(t) {
         t.plan(5);
         var map = new OpenLayers.Map("map", {
-            getExtent: function() {return(new OpenLayers.Bounds(-180,-90,180,90));},
+            getExtent: function() {return(new OpenLayers.Bounds(-180,-90,180,90));}
-            getProjectionObject: function() {return new OpenLayers.Projection("EPSG:4326");}
         });
+        var geographic = new OpenLayers.Projection("EPSG:4326");
 
         var a = new OpenLayers.Layer.WMS("dummy","http://localhost/wms", {
             layers: "a,b,c,d",
             styles: "a,b,c,d"
-        }, {map: map});
+        }, {projection: geographic});
 
         var b = new OpenLayers.Layer.WMS("dummy","http://localhost/wms", {
             layers: ["a","b","c","d"],
             styles: ["a","b","c","d"]
-        }, {map: map});
+        }, {projection: geographic});
 
         var c = new OpenLayers.Layer.WMS("dummy","http://localhost/wms", {
             layers: ["a","b","c","d"]
@@ -310,13 +310,13 @@
 
         var d = new OpenLayers.Layer.WMS("dummy","http://localhost/wms", {
             layers: "a,b,c,d"
-        }, {map: map});
+        }, {projection: geographic});
 
         var click = new OpenLayers.Control.WMSGetFeatureInfo({
             featureType: 'type',
             featureNS: 'ns',
             layers: [a, b, c, d]
-        }, {map: map});
+        }, {projection: geographic});
 
         map.addControl(click);