Leaking shower after shutting water heater valve

[foshizzle]

So my water heater started leaking and I shut off the valve on the pipe that feeds the water heater.

But water started coming out of the shower like someone hadn't turned it off. It is one of those hot/cold combined handle. You turn it clockwise to turn it off, and then spin it counterclockwise to turn it on, and it goes from cold to hot.

What is going on?

 

[breplum]

I’ve seen it happen especially on my own Price Pfister Avante shower valve. Why it happens doesn’t really matter because it’s something internal within the valve cartridge. Probably bad seals but most cartridges are not rebuildable, you just have to replace an entire cartridge

 

[foshizzle]

Is it because the water pressure is too much for the valve?

This bathroom was built 2 years ago. Is this a faulty install, or faulty cheap part?

 

[Geofd]

if its a single handle shower valve your still gonna get some flow
from the cold water inlet of the valve