Can't sync many_to_many relations from Wagon data to engine

Hello!

I have companies (~300) and categories (~100) in my project and they are in a N:M relationship. Everything works perfectly in Wagon project, but after I synced the data to Engine project the relationship won't work.

https://dl.dropboxusercontent.com/u/16954780/Locomotive/n_m_relation_seed.yml

(All the other content entries are synced correctly as well as 1:1, 1:N relationships.)

Many thanks for any answers!
Zsolt