Great Pix - and a case for a split - this story gets more and more interesting.
I have seen Pale Blue Flycatcher (male and female together) at Babao Shan and that one, which I guess is the most likely to turn up in HK, did have unbarred undertail coverts. 
L-Mike This is a very interesting bird - even if we don't know what it is yet - please do let us know where you saw it!
Mike K
							
							
							
													 
													
								Mike KilburnVice Chairman, HKBWSChairman, Conservation Committee