Example:

mikaeleiman@Berit ~/temp> ls
C#.tmbundle          jlink-test           s3stats
dmtp                 libusb-0.1.12.tar.gz
dmtp_corp            namnlös mapp
mikaeleiman@Berit ~/temp> cd namnlös mapp/
mikaeleiman@Berit ~/temp> cd ammnlös mapp/

I have a dir with a name containing a multi-byte UTF8 character, "namnlös mapp". When I type "cd n", the rest of the name is auto-complete-previewed (yay!). However, instead of the insert point being on "a", as you would expect, it's been moved back to "n". So when I type the second letter of the name, it overwrites the first letter, resulting in the last line of the example.