We have a Jandy No-Lube 3-way that splits the return water between the pool and the spa. The spa sits higher than the pool. There is no check valve on the return line to the spa. After the pump turns off, the Jandy allows water to back flow from the spa and back into the pool until the water level in the spa falls below the level of the return jets. Is the Jandy supposed to allow this to happen?