[EBB Sightings] Strange Duck at Lake Merritt, Oakland

Don't email me that a strange duck at Lake Merritt is not strange, I know.

At first glance, I thought I was looking at a male Hooded Merganser.  The 
bird was in a group of Barrow's Goldeneyes, and had some features that were 
similar to them.  It once surfaced in a group of Common Goldeneyes, and 
immediately departed for the Barrow's Goldeneyes.  Within the Barrow's 
Goldeneyes, there was some head-bobbing and some aggression among the males. 
  This bird participated in head-bobbing, but with another male, if indeed 
this bird is a male.

Description:
Size:
This bird was somewhat smaller than its companion goldeneyes.

Bill:
Bill was thin, merganser like, with a small hook at the end.  It seemed 
deeper than a merganser bill, especially at the base, but not as deep or 
sloped as the goldeneyes.

Head:
Head shape with its crest erect was similar to female goldeneyes, but 
larger.  Crest lacked the vertical front, and was rounder.  Color was a 
female goldeneye dark brown.  There was no white on the crest, as there 
should have been for hooded merganser.

Eye:
Eye was golden yellow, maybe too yellow for hooded.  I don't know how much 
variation there is, but seemed yellowier than Berkeley Aquatic hooded.

Breast:
Breast was white, with two vertical (almost) black bars.  This is consistent 
with hooded, as goldeneye has a short tab/spur which sometimes looks like a 
black bar if the bird is low in the water.

Flanks:
Side of the bird was gray, somewhat mottled, similar to male goldeneye.  
There was no apparent rufous color of a hooded.

Back:
Back was dark gray, and had white spots in it, rather further forward than a 
hooded, in which the white should show toward the rear.

As I said, this bird was with a flock of Barrow's Goldeneyes.  They were 
actively feeding at the SE corner of Lake Merritt, where the water comes in. 
  The inflow was quite strong, the tide within an hour of high.  I saw the 
bird 1/12 and 1/13 under the same conditions.  The second time, the bird was 
not with the flock when I arrived, but showed up in a few minutes by 
swimming from the northwest.  Therefore I think it remains on the lake, not 
in the Oakland Estuary or channel next to Laney College.

Mutant or Hybrid (If so, what x what) ???