When passing a default value for a field via context, you need to consider that this value can be passed on to models initially not planned for.
For example, when passing the product_qty as a default value in the manufacturing order, the value will propagate to the stock move as well, which may cause some unexpected issues, since it has the same field.
In such cases, the issue can be resolved by removing the default values from context, once they reach the initially intended model.