X not in slaves, yet still being used as a tasktracker

[Saptarshi Guha]

Hello,
A machine X which is the master: it is the jobtracker, namenode and
secondary namenode.
It is not in the slaves file and  is not part of the HDFSHowever in
the mapreduce web page, I notice it is being used as a tasktracker.
Is the jobtracker always a tasktracker? I'd rather not place too much
load on the one machine which plays so many roles.
(Hadoop 0.19.0)

Thanks
Saptarshi