[jQuery] malformed url with getJSON

I am using the following code to access the Yahoo Music API:
$.getJSON("http://us.music.yahooapis.com/artist/v1/list/
published/popular?
response=main&appid=myappid&format=json&callback=?",function(json)
{alert(json);});
and it generates the following url:

http://us.music.yahooapis.com/artist/v1/list/published/popular?response=main&appid=PISzAQ7V34Ee2_9eTnc28ZWc6Yn1aApPCr4_8lzDyRNqTzDeZjAtjNY2k4JgSqM-&format=json&callback=jsonp1230228631768&_=1230228631798
The last parameter (_=1230228631798) is created by jquery and the
Yahoo service flags it as a bad parameter.
The same occurs with the flickr example, but it seems that the Flickr
services just ignores it.
I have tried the url on a script tag so I'm sure it works. I wonder if
jquery converts the first and second '?' to callback functions and
that is why that extra parameter is created.
Is there someway to prevent jQuery from creating that extra parameter,
or is this a bug?
Thanks in advance for any help.
Mark