Pump Loses Pressure When Attaching Just The Surface Skimmer Hose

Scratching my head..

We just set up our new Intex Sand Filter Pump.
I followed all instructions on the Sand Filter Pump for start up. I backwashed the pump and rinsed as shown on the DVD that came with it. The pump runs perfectly until I attempt to attach the Intex Deluxe Surface Skimmer hose (not connected to the skimmer to the inlet hose adapter on the strainer connector inside the pool.

When I attach the Deluxe Surface Skimmer hose the pump basket starts filling with air (*from what I'm told, in pool lingo, that means the pump is "losing prime").

As soon as I disconnect the Deluxe Surface Skimmer hose from the inlet the pump basket chamber starts to fill back up and returns to normal (the prime returns to normal).

All hose attachments were checked over for tightness, any possible cuts or leaks. It all checks out fine.

The Intex Sand Filter Pump came with a new outlet that came with a valve. We already have valves on the shut off (plunger) valves for both the inlet and outlets.

Could the new outlet with valve attachment be causing the pump to lose prime when I place the Deluxe Surface Skimmer hose to the inlet adapter inside the pool?

My neighbor has the same Intex set up (sand filter, shut off plunger valves with valves and Deluxe Surface Skimmer), but does not have the new outlet with an adapter. His system works absolutely fine.

OUR SET-UP CONSISTS OF...
Pool: Intex 18' x 48" Ultra Frame Circular Pool
Pump: Intex Sand Filter Pump 2,150gph (Model SF70110-1)
Hooked into: Intex Saltwater System System (Model ECO7110)
*Both Plunger Valves have Air Release Valves on them.
*Sand Filter Pump came with new Inlet Valve (where the water shoots back into the pool) with additional Air Release Nozzle

I've attached photos..
https://i.imgsafe.org/32902b2b14.jpg
https://i.imgsafe.org/329373453e.jpg
https://i.imgsafe.org/3295943f05.jpg
https://i.imgsafe.org/3297622682.jpg