Windows default to wrong location

[avonside]

I am using trial version of Premier X3. I have changed wall type to a build-up of External brick skin, insulation batt, block inner skin, finish plaster. I have set the block inner skin as the main wall to ensure that internal walls connect properly, now when I insert windows they always position themselves within the block skin and not the brick outer skin.
Please can anyone tell me where I am going wrong ?