I have a filterinserter set to the other ore that empties the train. This just happens when the inserters have left overs on them when the train leaves. So the next train get this leftovers from the train before. It's easy to circuit when you have for example 4 or 5 different items. But i think this...

viewtopic.php?f=30&t=55529

tl;dr: They changed the fluidwagons from 3 individuell tanks to one tank and the code was not updated in all places for the api.