Make sure passed lsmask is not the same as cached mask

Author: nparley

lib/mpl_toolkits/basemap/__init__.py

@@ -3902,8 +3902,11 @@ def drawlsmask(self,land_color="0.8",ocean_color="w",lsmask=None,
         # or from plt.gca().
         ax = kwargs.pop('ax', None) or self._check_ax()
         # Clear saved lsmask is new lsmask is passed
-        if lsmask is not None or lsmask_lons is not None or lsmask_lats is not None:
-            self.lsmask = None
+        if lsmask is not None or lsmask_lons is not None \
+                or lsmask_lats is not None:
+            # Make sure passed lsmask is not the same as cached mask
+            if lsmask != self.lsmask:
+                self.lsmask = None
         # if lsmask,lsmask_lons,lsmask_lats keywords not given,
         # read default land-sea mask in from file.
         if lsmask is None or lsmask_lons is None or lsmask_lats is None: