mapred.tasktracker.map.tasks.maximum is not taking into effect

[praveen.peddi]

Hi all,
I am using hadoop 0.20.2. I am setting the property 
mapred.tasktracker.map.tasks.maximum = 4 (same for reduce also) on my job conf 
but I am still seeing max of only 2 map and reduce tasks on each node. I know 
my machine can run 4 maps and 4 reduce tasks in parallel. Is this a bug in 
0.20.2 or am I doing something wrong?

Configuration conf = new Configuration();
      conf.set("mapred.tasktracker.map.tasks.maximum", "4");
      conf.set("mapred.tasktracker.reduce.tasks.maximum", "4");

Thanks
Praveen