Problem with 2 warehouse and free shipping cost

[JrDeline]

PS 1.6.1.9 is currently running and so far only one warehouse has been used. Now a second warehouse has been added, which has been set up and also works perfectly. Furthermore, free shipping is offered for orders of € 50 or more.

Now it is the case that if an order is placed and contains items from both warehouses, the order comes in split up 2 times (one per warehouse), which is still ok, but if the order is split into the 2 warehouses and the order total for one Stock is below € 50, shipping costs will be offset. Which shouldn't be the case, since the order should be viewed as one and the customer therefore does not have to pay shipping from € 50.

I hope I wrote it so that you can understand the problem.

Did I forget something/somewhere in the settings, or did I set it wrong?