PR#5100 took on the task of changing information on setting mysql server defaults from UTF8 to utf8mb4. However doctrine does not actually obey this - at some point doctrine started explicitly setting column and table-level collation/charsets, and the value seems to be fixed (by default) to standard utf8.

Alternatives to force utf8mb4 for your entities require the following annotation:

@ORM\Table(options={"collate"="utf8mb4_unicode_ci", "charset"="utf8mb4"})

and while this seems hacky, it does the job.

There is aPR open for DoctrineBundle that should allow users to set a global option in their projects, although until this is merged, the documentation should be revised to remove this section as it may be dangerous for users relying upon it as the solution.