'who am i' command does not produce output in 'mrxvt'

[Countable Infinity <countableinfinity@gmail.com>]

'who am i' produces the following output in gnome-terminal:

humpty@nifty:~$ who am i
humpty    pts/2        2009-01-24 02:12 (:0.0)

However, in mrxvt, it does not produce any output.

humpty@nifty:~$ who am i
humpty@nifty:~$

What could be the reason for this? Is this a bug?