diff --git a/compass/ocean/tests/isomip_plus/viz/plot.py b/compass/ocean/tests/isomip_plus/viz/plot.py
index e231443a5c..c332b05f59 100644
--- a/compass/ocean/tests/isomip_plus/viz/plot.py
+++ b/compass/ocean/tests/isomip_plus/viz/plot.py
@@ -794,10 +794,10 @@ def _plot_horiz_field(self, field, title, outFileName, oceanDomain=True,
             return
 
         if oceanDomain:
-            localPatches = copy.copy(self.oceanPatches)
+            localPatches = copy.deepcopy(self.oceanPatches)
             localPatches.set_array(field[self.oceanMask])
         else:
-            localPatches = copy.copy(self.cavityPatches)
+            localPatches = copy.deepcopy(self.cavityPatches)
             localPatches.set_array(field[self.cavityMask])
 
         if cmap is not None: