social.msdn.microsoft.com/Forums/en-US/biztalkgeneral/thread/00fa8381-e308-43c2-adef-7848bf1f17bd/
Send port filter expression use the properties in the message context, when you promote the fileds it won't become context properties unless you do it in the poperty schema. For this you have to edit the property schema and make the source(promoted field)'s MessageDataPropertyBase=MessageContextPropertyBase and then redeploy and make the filter. You should also be able to see the source propery in the Message context properties.