I am working through a fairly large upgrade at the moment and as part of this, there will be some content restructuring. The customer wants to retain the original urls for now but the original content has dropped one level deeper in the content hierarchy and so I've written a UrlProvider to remove the new segment of the url. The problem is that all nodes this gets applied to now have an error:

This document is published but its url would collide with content (error)

I can see no reason why there should be a collision since the content that was at the url is no longer there. Any ideas why this might be failing?

The UrlProvider is as follows:

public class MyUrlProvider : DefaultUrlProvider
{
    public MyUrlProvider()
        : base(UmbracoConfig.For.UmbracoSettings().RequestHandler)
    {            
    }

    public override string GetUrl(UmbracoContext umbracoContext, int id, Uri current, UrlProviderMode mode)
    {
        // Take curent content item from cache by its id
        var content = umbracoContext.ContentCache.GetById(id);
        var route = umbracoContext.ContentCache.GetRouteById(id);

        // Check if the content exists and it has alias companyItem
        if (content != null && route.StartsWith("/segment-to-remove/"))
        {
                var segments = route.Split(new[] { '/'}, StringSplitOptions.RemoveEmptyEntries);                
                var newSegments = segments.Skip(1);
                return string.Join("/", newSegments.ToArray()).EnsureStartsWith("/").EnsureEndsWith("/");
        }

        return null;
    }
}