The sound that the slider controls is can be heard as two parts - there is a high frequency part and a lower frequency part. We have found through our studies that using two parts for a fuller sound is easier for the user to listen to for longer periods.
When you move the slider to adjust the balance of your therapy sound (left ear/right ear), you are only moving some of the higher frequency sound. The lower frequency sound stays evenly balanced in addition to some of the higher frequency sound that stays on the side not chosen.
There may be an issue where you are not able to hear the higher frequency sound as well on the chosen side (tinnitus is usually related to hearing loss at the tinnitus frequency) compared to the other side. This is absolutely normal.
Even though it sounds like you are hearing the sound in the right ear only, the affected side is reacting to the therapy as well.