Yellow or Citrine(?) Wagtail

First winter Wagtail, seen at the saltpans in Fuencaliente

A tricky one. This first winter Wagtail was found at the saltpans in Fuencaliente on Sep 12. My first impression (and hope!) was that this bird could be a Citrine Wagtail (Motacilla citreola). The two broad white wingbars are very contrasting, there appears to be a pale border around the cheeks, and there is no hint of yellow anywhere in the plumage, not even near the vent.

The upperparts are entirely grey, with no hint of olive tones; the lores are pale rather than dark.

But (and this is a big one), the lower mandible of the bird's bill is pale: in Citrine Wagtail (Motacilla citreola), the bill should be all dark. (Martin Garner's blog "Birding Frontiers" does mention the existence of Citrine Wagtails with pale-based bills, however).

The overall shape of the bird, which has a shortish tail (not long enough for Citrine), plus its observed "run-picking" feeding technique point towards Yellow Wagtail (Motacilla flava), rather than Citrine (M. citreola). So, I'm staying with that verdict.

Not quite sure how to interpret the blotches on the bird's breast, visible in the above image.

Second opinions are always welcome: any comments helping to confirm this bird's identity will be greatly appreciated.

So far (Oct 25), all expert opinion received has favoured Citrine (M. citreola), rather than Yellow Wagtail (M. flava).