add repro scene for PR 195.

tests/usda/composition/issue-195-ref.usda

@@ -0,0 +1,21 @@
+#usda 1.0
+
+( defaultPrim = "a" )
+
+def Xform "a"
+(
+    kind = "component"
+    assetInfo = {
+	asset identifier = @assets/Refridgerator/Refridgerator.usd@
+	string name = "Refridgerator"
+    }
+    #payload = @./Refridgerator_payload.usd@</Refridgerator>
+    variants = {
+	string modelingVariant = "Decorated"
+    }
+    prepend variantSets = ["modelingVariant"]
+)
+{
+
+}
+

tests/usda/composition/references-prepend-195.usda

@@ -0,0 +1,19 @@
+#usda 1.0
+
+( defaultPrim = "a"
+
+"""
+repro scene for https://github.com/lighttransport/tinyusdz/pull/195
+Issue 195: base properties(e.g. 'HelloWorld') disappear after `--flatten`.
+"""
+)
+
+def "a" 
+(
+    prepend references = @./issue-195-ref.usda@
+)
+{
+    string HelloWorld = "Hello World"
+    double3 xformOp:translate = (259.9341506958008, 95.84612274169922, -0.5277154445648193)
+    uniform token[] xformOpOrder = ["xformOp:translate"]
+}