Tone function bug or not?

Anyone run the Tone function under 31Hz? I tried only the line tone(pin,30) and no other code and the output is some random frequency. From 0-30Hz it does this. It might be 1200Hz at 30 then 500Hz at 28. Is this a possible bug? I tried to look at the code library but I don't understand the low level stuff. Search for "Ugly Details"

Thanks coding badly, sometimes searching will take days to find answers. I don't understand why this is not spelled out in the main site tone reference. I did download that library before but never read all the details because I didn't use it yet. I will try that library then.