Since all your business activities occur while you are working remotely in WA, then this would all be considered WA sourced income. If you do eventually have MT sourced income (from doing business while actually being in MT), since you are a resident of WA, you would only have to include MT-sourced income on your MT nonresident state income tax return. No part of your WA salary earned in WA would need to be included on your MT nonresident state income tax return.
