Sorry for the delay in the reply. From what you're describing it sounds you have set a "home channel" in your settings. What the home channel does is every time you log into your Slingbox it will automatically tune to that channel. To turn this feature off you will need to tab on settings when logged into your account via your iPhone and you will see "Home Channel" and can adjust your settings there.
If you have any further questions please fell free to reply to this post.
Sling Media moderation Team