Tree identical variables - 3 differen linker errors

[bobef]

I have the following variables

extern GLboolean _GLEE_WGL_OML_sync_control;
GLboolean _GLEE_WGL_I3D_swap_frame_usage;
extern GLboolean _GLEE_WGL_3DL_stereo_control;

first one is ok. no error.
and for the last two I get these errors

GLee_h.obj(GLee_h)  Offset 17069H Record Type 0091
  Error 1: Previous Definition Different : __GLEE_WGL_I3D_swap_frame_usage

GLee.obj(GLee)
  Error 42: Symbol Undefined __GLEE_WGL_3DL_stereo_control

if I make the second one extern it works. If I make the third one not 
extern it works too.
everything about these variables (except the names) is absolutely 
identical. What is wrong?