When the flaps are deployed, the reason WAI is not selected with a manual system (SOPs) or selected off automatically with the Auto system, is the fact that the leading edge looses the majority of airflow over it, as it gets covered by the LE flaps.
http://www.airliners.net/open.file/228836/L/
http://www.airliners.net/open.file/289926/L/
All that ends up happening is the possibility of overheating the LE which as you probably know is only made of aluminium as opposed to the spray tube which is made of titanium, like the bleed ducts.
Hope this sorts it out.