Arming whilst exit door is open

Hi, I've run into a small but irritating issue. We have the system covering our garage/workshop. With our old alarm it would allow us to arm the system with the main door open (we often leave the door open when using the workshop so its a bit annoying to have to close it to arm the system) and then we could walk out, close and lock the door, no problem. It seems that with this system I have to bypass the door sensor in order to do this, which negates the point of the door sensor if it's not activated! Please help! Thanks.