A leaky faucet thread

At my home we have an annoying problem with the bathroom sink leaking when the hot water is turned on. The sink has knobs for hot and cold water. Turn the hot water's main knob on from below the sink and no matter how off the actual sink knob is, the faucet runs. So if you need hot water you have to turn it on from below the sink, use it, and turn it back off. The cold water has no problems.

Help! Surely someone in this crazy land of INTERNET can help!

>>1
Just so you know, that below-the-sink valve is a LOT less reliable for daily use as is the top tap valve.  Using it like that will just make it leak, most likely.  Then, you're fucked, and your lazy ass will have to repair TWO VALVES where before you only had to repair one.  Good job!  Typical American thinking, right there.