Water in venturi line of HOB skimmer

[dmolavi]

I just fed my tank, shutting down the skimmer (Eshopps PSK-75H) before, and turning it on after. I noticed that when I unplugged it, water filled into the airline, which I didn't think was supposed to happen. I have the airline in it's normal "upright and locked" position, so the top of it is well above the water line.

Any ideas what could be causing this?

 

[dmolavi]

I should add that when I restart the skimmer, the water is obviously sucked out, but I don't think it should be in there to begin with...