You can't request the same Item in multiple slots.
So one Loco in Slot 1 and two Locos in Slot 2 will give you an Error-Message.
If you try to put the 2 Locos in slot 2 you'll get this:
Locomotive is already requested on another slot.

Thanks,

Unfortunately I cannot think of a simple fix, and don't want to ask the dev's to re-enable this feature. The correct fix is for me to learn to use GUI's and make it work properly, but that is going to be a slow process.

Got that.

I like this mod because it doesn't create trains out of air...
Keep it up ;)

Have a good start into the new year!