Fish's remark in the linked thread made me do some quick testing, using DyTech-Transportation. The problem still occurs, but it's less frequent when there's one high speed cargo wagon hooked up to the train and less frequent again with two cargo wagons. All the while, top speed for the train is still the 2.00, but the cargo wagons do have an effect.
I don't have OCD, I have CDO. It's the same, but with the letters in the correct order.