If I start the application with command line parameters that will make
it try to get fullscreen mode, then:
- the current layout of the workspace is ignored, and the xpdf window
indeed fill the whole workspace.
- the keys for cycling through windows in the current workspace are
ignored. (keys for switching to another workspace still works).
This is symptomatic of a window that is not being managed, i.e. it uses override_redirect. In the case of rdesktop, you should not use -f; try -D -K possibly along with a layout that supports managed fullscreen (XMonad.Layout.Fullscreen in darks XMonadContrib).