When I select "Save As" and change "Save as type" to let's say ".txt" then the content of the "Filename" field get's highlighted. (And you expect this field to be focused.)
But when I then start typing the field name, the "Save as type" changes instead, which is very annoying.
A more logic setup would be that after changing "Save as type", focus is set on the "Filename" field.
Program used: WeBuilder 2015 v13.2.0.164