This question is more of I'd like to know rather than an issue for me right now.
In the table exp_channel_data Playa fields store a string using the following fields from the relationship channel entry: "[entry_id] [url_title] title".
However the table exp_playa_relationships is the one that stores the IDs between parent, child etc. This is the only table that is updated if one of the entries are edited. So why is the string stored in the exp_channel_data table?