Bathroom faucet- leaks into cabinet when backpressure created

I discovered a problem last night with my bathroom faucet. If you have it on and hold a towl or something up to the water, forcibly stopping the water (I was rinsing out a hand towl and trying to force water through it), then underneath it leaks/sprays. The leak is coming from the plunger that you pull up/push down to plug/unplug sink.
Is this normal for a sing to do this? The sink/house is only 4 years old. I have not tested this in other bathrooms yet.
Thanks in advance for any thoughts/ideas. -Clayton
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Dooler wrote:

It only looks like it is coming from the lift rod/plunger. After the faucet is secured/sealed to the sink, there is a small opening for the rod to go thru. If any water leaks under the faucet base, it will drip out thru the opening for the rod.
Many single-handle faucets have a spout design which is open on the bottom side, or at least not sealed. So, any water which splashes or is forced underneath can get under the faucet base, where it can leak thru the rod opening.
Take a look at the bottom of the spout to see if this is true of yours. You may be able to caulk the space where the spout meets the base but it's basically a design problem.
Jim
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I agree with the fact that it is a design issue, not necessarily a problem. In most bathroom faucets the water is carried to the aerator through a small tube. The pretty outside that you see is mostly for decoration. As mentioned, when you force water 'backwards' as you describe, it is forced around the aerator and into the cavity between the supply stube and the faucet housing. If the plunger rod goes through this housing, that's where the water is likely to find an exit.

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