Hello,

With sed from git (4.2.2.89-e387), I get one test failure in 'invalid-mb-seq-UMR' (log attached).

The error seem to be:
===
+valgrind --quiet --error-exitcode=1 sed -e 's/a/b\U\xb2c/' in
[...]
+ compare_ exp out
+ diff -u exp out
--- exp 2015-07-23 17:42:41.144358380 -0400
+++ out 2015-07-23 17:42:41.780358374 -0400
@@ -1 +1 @@
-bC
+b<FF>C
===

regards,
  - assaf