diff --git a/README.md b/README.md
index f59191b..efb0cbc 100755
--- a/README.md
+++ b/README.md
@@ -732,6 +732,9 @@ mixinFlat(<base>, <object>, ..)
 This is like `Object.assign(..)` but copies property descriptors rather 
 than property values.
 
+Also like `Object.assign(..)` this _will_ overwrite attribute values in 
+`<base>`.
+
 
 ### `RawInstance(..)`
 
diff --git a/test.js b/test.js
index 11fce24..a685745 100755
--- a/test.js
+++ b/test.js
@@ -633,6 +633,8 @@ module.modifiers = {
 		return res },
 
 	// mixins...
+	// NOTE: running this in flat mode will have side-effects -- overwriting
+	// 		existing attributes and methods...
 	// XXX might be a good idea to get the method name from the context... how?
 	mixin_instance: function(assert, setup, flat, filter, get){
 		filter = filter || instances