diff --git a/layout/base/nsDisplayList.cpp b/layout/base/nsDisplayList.cpp
index d3c7ffbe6261..6e4d05c67885 100644
--- a/layout/base/nsDisplayList.cpp
+++ b/layout/base/nsDisplayList.cpp
@@ -2065,6 +2065,9 @@ nsDisplayBackgroundImage::IsVaryingRelativeToMovingFrame(nsDisplayListBuilder* a
 nsRect
 nsDisplayBackgroundImage::GetPositioningArea()
 {
+  if (mIsThemed) {
+    return nsRect(ToReferenceFrame(), mFrame->GetSize());
+  }
   if (!mBackgroundStyle) {
     return nsRect();
   }
@@ -2138,7 +2141,7 @@ void nsDisplayBackgroundImage::ComputeInvalidationRegion(nsDisplayListBuilder* a
                                                          const nsDisplayItemGeometry* aGeometry,
                                                          nsRegion* aInvalidRegion)
 {
-  if (!mBackgroundStyle) {
+  if (!mIsThemed && !mBackgroundStyle) {
     return;
   }
 
diff --git a/layout/reftests/bugs/828146-1-ref.html b/layout/reftests/bugs/828146-1-ref.html
new file mode 100644
index 000000000000..f5ec280a992b
--- /dev/null
+++ b/layout/reftests/bugs/828146-1-ref.html
@@ -0,0 +1,6 @@
+<!DOCTYPE HTML>
+<html>
+<body>
+<div style="width:100px; height:100px; position:relative; top:60px; -moz-appearance:button"></div>
+</body>
+</html>
diff --git a/layout/reftests/bugs/828146-1.html b/layout/reftests/bugs/828146-1.html
new file mode 100644
index 000000000000..e196c5f8c88e
--- /dev/null
+++ b/layout/reftests/bugs/828146-1.html
@@ -0,0 +1,14 @@
+<!DOCTYPE HTML>
+<html class="reftest-wait">
+<body>
+<div id="b" style="width:100px; height:100px; position:relative; top:50px; -moz-appearance:button"></div>
+<script>
+var b = document.getElementById("b");
+function doTest() {
+  b.style.top = "60px";
+  document.documentElement.removeAttribute("class");
+}
+window.addEventListener("MozReftestInvalidate", doTest, false);
+</script>
+</body>
+</html>
