When I run PuTTY (a window ssh client) via an rdesktop session, the mouse pointer turns black inside my PuTTY window which has a black background, rendering it invisible. (Unless I move it over some text so I can see the shadow.)
Solution:
The workaround is to change the "Text Select" pointer on the Windows machine by going to Control Panel->Mouse->Pointers. I changed it to the beam_r.cur image, which is a beefier version of the I-beam bitmap which does render nicely in rdesktop.