text is not transparent

[relaxslow]

I 'm new to LWJGL and feel it good. I build my UIObj  class use the method in bood "3d game development with LWJGL" chapter twelve and it should transparent because I have already add the following lines
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

but the two UI Obj seems not transparent when they overlap. Their background are glclearColor which I set at the beginning of the program.
Did anybody meet this situation?