While trying to develop a new Symfony frontend to an existing database - whcih unfortunately contains non-ascii character names - I ran into a lot of problems where non-ascii characters had been mangled.
After installing XDebug and digging into the issue I found that the use of strtolower on the column names was the issue, since it's not safe to use on UTF-8 strings.
I replaced all calls to strtolower with mb_strtolower and UTF-8 encoding which solved my issue. I don't know if that is the correct way of doing it or if there is a better way.
I saw one other use of mb_strtolower in doctrine and it was guarded with an if function exists... Also it might be an issue in other files as well...
I provide my patch file incase it is of any use.