[ESS] ESS SAS function keys in mrxvt

[duckpond]

The following setting (in .emacs) works just fine in xterm:
 (setq ess-sas-global-unix-keys t)

But with my more preferred terminal mrxvt 0.5.1, it seems not working, i.e.,

F1 through F4 will just type a tilde "~" in the buffer, F8 brings to shell
(won't submit), F5 the log, F6 gave output, etc.

Also tried (setq ess-sas-global-pc-keys t) to no avail. 

It's more like a terminal-dependent problem, am I right? Any suggestions?

Thanks,

Jindan