As promised, I now have photos of both the 777 and 787 CW seats.

These are the 777 seats. The first shows the footrest in the low position:



The second shows the footrest in the upper position:



The last has it halfway, but angled as in what the seat instructions call "the Z position':



On these seats, the latch pressed on the footrest handle releases the middle part of the bit which supports the footrest (marked in red):



This part seems to be some form of belt which the footrest is attatched to and which can move up and down, thus altering the position of the footrest.

The 787 seat works differently though.

Here is the footrest in the high position:



Here is the footrest in the low position:



The red line marks the latch which attaches the footrest to its support.

Another view of this latch with the seat in the upper position, but pulled away from the support a little:



This support gets jammed into the support and is extremely difficult to release. It can be done by pulling the seat away a little from the support and fiddling around. With a little poersistence it can be 'freed'. Now what is strange is that I have never had any problems when sitting in the middle seats, only in the aisle seats! In fact, on my last trip I was in 7E and the footrest was fine. Nobody was sitting in 7D so I had a look there and sure enough the footrest was jammed.

What is clear beyond any doubt is that the mechanisms of the 777 and 787 seats are completely different.