Connection.UnitOfWork::buildFlushTree when loading data from yml file, Incorrect ordering of tables by their relations

I don't know where exactly to start, I'm new here, and i'm not even sure this is a bug. BUT

We have a database structure with most important tables' PK's as string fields, which function as FK on other tables the basic structure is:

Artist
-Album
-Song
-Comments

each artist has multiple songs
each artist has multiple albums
each album has multiple songs that belong to the same artist as the album belongs to
each song has multiple comments

thus, the UnitOfWork - builtFlushTree should generate

[0]=>Artist
[1]=>Album
[2]=>Song
[3]=>Comments

but instead i get:
[0] => Album
[1] => Artist
[2] => Song
[3] => Lyrics

which in turn generates:

QLSTATE[23000]: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails (`lyrics`.`album`, CONSTRAINT `album_artist_fk_stripped_name_artist_stripped_name` FOREIGN KEY (`artist_fk_stripped_name`) REFERENCES `artist` (`stripped_name`) ON DELETE CASCADE ON UPDATE CASC)
obviously.

I've been going through symfony/doctrine code for a whole day trying to figure out why I can't load-data. in the end i get to this buildFlushTree function.
probably have to go deeper. but so far this is it

PS. It's my decision to use string fields as PK's and FK even though it's a bad practice, but just because it is a bad practice I shouldn't be unable to work with it.