That is kind of odd. I had this as well but I ran planeshift from the commandline with the -relight option and it fixed it. took a few hours though to finish.
[bill@billbox ~]$ planeshift --help
Your configuration files are in... /home/bill/.PlaneShift
DEBUG: Sound System Software Renderer Initializing...
Options for Crystal Space 2D driver for OpenGL using GL/X:
-depth=<val> Display depth (32)
-[no]fs Fullscreen if available (no)
-mode=<val> Window size or resolution (1440x900)
Options for Crystal Space 3D Engine:
-fov=<val> Field of Vision (0)
-[no]relight Force/inhibit recalculation of lightmaps (no)
-renderloop=<val> Override the default render loop ()
General options:
-help this help
-canvas=<s> the 2D canvas driver (asciiart, x2d, ...)
-cfgfile=<file> load a configuration file
-cfgset=<key=val> specify a configuration setting
-plugin=<s> load the plugin after all others
-verbose be more verbose; print better diagnostic messages
-video=<s> the 3D rendering driver (opengl, software, ...)
]/code]
You could also try relighting the specific map from the planeshift-setup utility. I am not certain that works but it used to.