I got myself a DHT22 from Amazon.com. Temperature seems to be very accurate, but the humidity values are way off. I checked it with 2 other thermometers/hygrometers. Both show values between 62 and 65% in the living room (which makes sense) while the DHT22 shows 31% (very unlikely).
Is this a known issue of the DHT22?
Yes, I've seen them read both 20% high or low. I just replaced my last one a few hours ago with an Adafruit SHT31-D breakout board. It's very easy to connect, has a nice library and example, and is unusually stable.
just the bare sensor or a breakout board? If a bare sensor did you solder it?
Breakout
You can check calibration by using table salt as a slush with water.
If you have the sensor in a plastic bag with a disk of this slush,
it will create a humidity of 75%. If higher, the salt will absorb moisture.
If below moisture will evaporate.
I would not believe any other reference electronic reference.
There are other calibration salts available for other humidity percentages.
Dwight