Nothing to do with Mangala (whose future won't be settled till after the World Cup and even then it's not just a fee with Porto that has to be agreed, the player has to be convinced), it's some payment dispute.
It'd help if someone who could read Portuguese well could translate that article (<a class="postlink" href="https://pbs.twimg.com/media/BqKrlZyCQAA71GA.jpg:large" onclick="window.open(this.href);return false;">https://pbs.twimg.com/media/BqKrlZyCQAA71GA.jpg:large</a>) because the online version is behind a pay wall. However, the deal still seems most likely to go through once it's sorted, the player probably just got sick of sitting around waiting for suits to sort out details so went back to his holidays (which he had cut short to sign for City). He'll probably be on the first plane over when it's sorted.