diff --git a/docs/change-log.md b/docs/change-log.md
index 7ec773c3..1627c459 100644
--- a/docs/change-log.md
+++ b/docs/change-log.md
@@ -17,6 +17,7 @@
 -	set promise's default value to initialValue if coming from m.request [#454](https://github.com/lhorie/mithril.js/issues/454)
 -	fix dom element ownership bug when mixing keyed elements and third party plugin elements [#463](https://github.com/lhorie/mithril.js/issues/463)
 -	fix edge case in flatten algorithm [#448](https://github.com/lhorie/mithril.js/issues/448)
+-	prevent unnecessary DOM move operation when mixing keyed and unkeyed elements [#398](https://github.com/lhorie/mithril.js/issues/398)
 
 ---
 
diff --git a/mithril.js b/mithril.js
index f9ab73ee..1a2742df 100644
--- a/mithril.js
+++ b/mithril.js
@@ -137,6 +137,10 @@ var m = (function app(window, undefined) {
 					existing[cached[i].attrs.key] = {action: DELETION, index: i}
 				}
 			}
+			var guid = 0
+			for (var i = 0, len = data.length; i < len; i++) {
+				if (data[i] && data[i].attrs && data[i].attrs.key == null) data[i].attrs.key = "__mithril__" + guid++
+			}
 			if (shouldMaintainIdentities) {
 				if (data.indexOf(null) > -1) data = data.filter(function(x) {return x != null})
 				
@@ -212,7 +216,7 @@ var m = (function app(window, undefined) {
 					//fix offset of next element if item was a trusted string w/ more than one html element
 					//the first clause in the regexp matches elements
 					//the second clause (after the pipe) matches text nodes
-					subArrayCount += (item.match(/<[^\/]|\>\s*[^<]|&/g) || []).length
+					subArrayCount += (item.match(/<[^\/]|\>\s*[^<]/g) || [0]).length
 				}
 				else subArrayCount += type.call(item) === ARRAY ? item.length : 1;
 				cached[cacheCount++] = item