The default shader is just that, it is a default shader which the system uses kind of as a blank slate.  If you increased shininess or reflection, or even highlights on the default.  It would only affect objects which still were using the default shader.  Creating new shaders for them or assigning premade ones would solve that.  It is difficult to diagnose without seeing the problem.  If you can snag a screen shot, or better yet, do a quick full render at like 640x480 and send it up, then we could probably help more.