When it's cheaper and easier to pull MORE gold out of the ground, that's not strictly speaking a fixed money supply.
When Rome (the empire) dumped a whole bunch of new found (stolen) gold on Rome (the city) that caused inflation too.
If your money supply is growing - it's growing.
Now if you have far too lose a monetary policy and you're inflating the money supply way too much and way too fast, that can be disastrous.
But if Alan Greenspan had found a way to convert led into gold, we would have gotten the real estate bubble even with a gold standard.