Bad Valve or Check Valve?

[ohpoolboy]

I have a spill over spa that is 18 inches above my pool. My plumbing setup is attached. When the return water from the the filter is directed to the spa and the pump is turned off, the spa will drain down to the spa drain level. This happens whether the spa is getting water from the pool (spillover mode) or isolated from the pool (suction from the spa - return to the spa).

I do not have any check valves installed on the plumbing. I'm wondering if this is; a) normal, b) due to a bad 3-way valve c) due to the lack of a check valve d) some other problem.

Any ideas?