Trust your hydrometer.
If the temp of the wort changes, you can see bubbles coming out the airlock as CO2 is released. You've probably also noticed it bubbles when you move it, because CO2 comes out of solution.
You want a stable hydro reading over the course of a few days. If you have that, then you're fine. Don't worry about the airlock.
Edit: Beaten by a minute!
"I can't believe how many people think Air Lock is pronounced Hydrometer." -BigKahuna
"If you gave me a beer with placenta in it without telling me I would kick you in the nuts." -ODaniel
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