Shader multiplying on its own
I'm currently using Maya 2019 and I've noticed that a Lambert shader is multiplying whenever I apply any shader or texture to my geometry.
I've included two screen shots to illustrate the issue.
As you can see, in the Hypershade there is only one Lambert shader. However, when I apply shaders from the screen option the Lambert shader just keeps multiplying and I can't delete them. Eventually I have dozens of the same shader in the list which causes issues when applying the shaders that I do need.
I would like to know if anybody has any idea as to why this is happening?