Don't replace thumbnails with placeholders.

library/src/main/java/com/bumptech/glide/request/ThumbnailRequestCoordinator.java

@@ -20,7 +20,7 @@ public class ThumbnailRequestCoordinator implements RequestCoordinator, Request
 
     @Override
     public boolean canSetPlaceholder(Request request) {
-        return request == full;
+        return request == full && !isAnyRequestComplete();
     }
 
     @Override

library/src/test/java/com/bumptech/glide/request/GenericRequestTest.java

@@ -572,7 +572,7 @@ public class GenericRequestTest {
     }
 
     @Test
-    public void testCallsEngingWithOverrideWidthAndHeightIfSet() {
+    public void testCallsEngineWithOverrideWidthAndHeightIfSet() {
         harness.overrideWidth = 1;
         harness.overrideHeight = 2;
         GenericRequest<Object, Object, Object, Object> request = harness.getRequest();
@@ -584,6 +584,16 @@ public class GenericRequestTest {
                 any(Priority.class), anyBoolean(), any(ResourceCallback.class));
     }
 
+    @Test
+    public void testDoesNotSetErrorDrawableIfRequestCoordinatorDoesntAllowIt() {
+        harness.errorDrawable = new ColorDrawable(Color.RED);
+        GenericRequest<Object, Object, Object, Object> request = harness.getRequest();
+        when(harness.requestCoordinator.canSetPlaceholder(any(Request.class))).thenReturn(false);
+        request.onException(new IOException("Test"));
+
+        verify(harness.target, never()).setPlaceholder(any(Drawable.class));
+    }
+
     private Context mockContextToReturn(int resourceId, Drawable drawable) {
         Resources resources = mock(Resources.class);
         Context context = mock(Context.class);

library/src/test/java/com/bumptech/glide/request/ThumbnailRequestCoordinatorTest.java

@@ -80,4 +80,20 @@ public class ThumbnailRequestCoordinatorTest {
 
         verify(thumb,never()).run();
     }
+
+    @Test
+    public void testDoesNotAllowThumbToSetPlaceholder() {
+        assertFalse(coordinator.canSetPlaceholder(thumb));
+    }
+
+    @Test
+    public void testAllowsFullToSetPlaceholder() {
+        assertTrue(coordinator.canSetPlaceholder(full));
+    }
+
+    @Test
+    public void testDoesNotAllowFullToSetPlaceholderIfThumbComplete() {
+        when(thumb.isComplete()).thenReturn(true);
+        assertFalse(coordinator.canSetPlaceholder(full));
+    }
 }