Invalid cast in Commerce Manager after update from 11.2.5 to 11.8.5

Hi all,

After upgrading from Commerce 11.2.5 to 11.8.5, which should not contain any breaking change, we get the following error in Commerce Manager when trying to create a return. Anyone seen this error? Is this an undocumented breaking change?

[InvalidCastException: Unable to cast object of type 'EPiServer.Commerce.Order.Internal.InMemoryShipment' to type 'Mediachase.Commerce.Orders.Shipment'.]
EPiServer.Commerce.Order.Calculator.DefaultShippingCalculator.GetShippingRate(IShipment shipment, ShippingMethodRow row, IMarket market) +282
EPiServer.Commerce.Order.Calculator.DefaultShippingCalculator.CalculateShippingCost(IShipment shipment, IMarket market, Currency currency) +575
EPiServer.Commerce.Order.Calculator.DefaultShippingCalculator.GetDiscountedShippingAmount(IShipment shipment, IMarket market, Currency currency) +388
EPiServer.Commerce.Order.Calculator.DefaultTaxCalculator.CalculateShippingTaxTotal(IShipment shipment, IMarket market, Currency currency, Func`3 getShippingTotalFunc, Func`3 getDiscountedPriceFunc, Boolean isReturn) +311
EPiServer.Commerce.Order.Calculator.DefaultTaxCalculator.CalculateShippingTaxTotal(IShipment shipment, IMarket market, Currency currency) +259
EPiServer.Commerce.Order.Calculator.DefaultTaxCalculator.GetShippingTaxTotal(IShipment shipment, IMarket market, Currency currency) +367
EPiServer.Commerce.Order.Calculator.<>c__DisplayClass7_0.<GetTotalForReturns>b__1(IShipment shipment) +157
System.Linq.WhereSelectEnumerableIterator`2.MoveNext() +233
System.Linq.Enumerable.Sum(IEnumerable`1 source) +98
EPiServer.Commerce.Order.Calculator.DefaultReturnPurchaseOrderCalculator.GetTotalForReturns(IPurchaseOrder order) +788
EPiServer.Commerce.Order.Calculator.DefaultReturnPurchaseOrderCalculator.CalculateReturnTotal(IPurchaseOrder purchaseOrder, IReturnOrderForm currentReturnForm, Boolean isCompletingReturnForm) +338
Mediachase.Commerce.Manager.Apps.Order.Modules.OrderCreateReturn.CalculateReturnTotal() +147
Mediachase.Commerce.Manager.Apps.Order.Modules.OrderCreateReturn.Page_Load(Object sender, EventArgs e) +1241
System.Web.UI.Control.OnLoad(EventArgs e) +106
System.Web.UI.Control.LoadRecursive() +68
System.Web.UI.Control.LoadRecursive() +162
System.Web.UI.Control.LoadRecursive() +162
System.Web.UI.Control.LoadRecursive() +162
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +3785