This is actually from Lorax, but the package is the same at the present time (pdksh-5.2.14-1). PS1 is set to be [\u@\h \W] but ksh isn't interpreting them as special sequences and leaving that verbatim as the prompt. This is due to the fact that ksh reads /etc/profile as it's startup file as well as bash and the two don't share identical syntax.
This will be fixed in setup-2.1.6, as the prompt will be set in /etc/bashrc.