In the new update 7.00.04 the roughness/glossiness slider stops working if you tick “use roughness”. Doesn’t work either if you tick it off. You will have to create a new material to get it working again. and then the same bug happens again if you tick on/off.
I still can’t reproduce it. There must be something else in the shader causing it, since it doesn’t seem to happen on a default material with white reflection. Could you try to reproduce it on a simple scene?