Strange warning message: the object with an index of 0 has been declared twice

In recent OpenBVE builds (1.7 and up) RouteViewer gives me an error message that I don't really understand:

The object with an index of 0 has been declared twice. The most recent declaration will be used.



It doesn't refer to a specific object. I checked everything to see if I mistakenly declared an index twice but couldn't find any errors. The route where I have this problem is here (I quickly put it inside a .7z archive):

https://drive.google.com/open?id=1EBVLGVxlTqq2WcpvRDJG9msmfRLKg1Mr

OpenBVE 1.6 and before doesn't produce this error message.

Can anyone help me figure this out?

Interesting (and harmless....)

This is being caused by the Structure.Pole declaration.
The trouble here is that openBVE has internal 'compatability' poles, which occupy indices 0 through 3.
By declaring a new pole using index 0, you're overwriting this inbuilt one and triggering the warning.

The error message needs to be made a little more specific (which specific object type for starters), and probably fine-tuned to exclude the default poles somehow, but it's valid.

Thanks. I'll just use a diferent index number then.