What is way 32773976, is it useful ?
The reason I ask is that it overlaps an area I am editing a lot and causes the background in JOSM to be grey rather than black, which reduces contrast.
I seem to have edited this way at some point, but not intentionally.
Note that if you switch to wire frame view in the view menu, the contrast issue will go away (along with some other useful stuff unfortunatly)
I’m rather new here, so can’t actaully help with your main question i’m afrade 
Just look at the history of the way :
http://www.openstreetmap.org/browse/way/32773976/history
Ask the user who created the boundary (btw: what kind of boundary should that be ?) :
http://www.openstreetmap.org/user/Steve%20Chilton
Boundary Yahoo is used to inform other users where the limits of detailed Yahoo! Aerial imagery lies. I came across one of those yesterday near Bath.
You might want to ask the user whether the area=yes can be removed. It seems that this is what causes the grey rendering in JOSM. Imo it’s wrong anyway because that way doesn’t represent an area - it’s the boundary of an area. Also, boundary=* is documented to be used on ways, not areas.
Of course, I usually wouldn’t suggest changing to change the tagging of something because of rendering style problems in an editor. Yahoo boundaries, however, don’t serve a purpose except (supposedly) assisting mappers, so if they make editing harder, they are worse than useless.
Thanks all. I now know what it is and why it has the effect it does in JOSM. That gives me a short term workround of removing the area=yes tag locally while editing, replacing it before uploading changes (with minimal damage if I forget!). Longer term I can work with the original author.
As the boundary is a single closed way, it is easy enough to tell the inside (area with imagery) from the outside without the need for shading.