Headphones: no difference cue - mixing

Hello.

I have a question. I have a DDJ-400 controller. When I plug my headphones in and listen while trying to mix two song, I've noticed that there is no difference between the headphone function cue and mixing on my DDJ-400. I've tried both settings true the scroll button on my DDJ-400, but there is no difference between the two. I'm not quite sure, but in my memory there was a difference before. Should there be a difference in hearing between the function cue and mixing? I guess there should be (because why would there otherwise be three functions: cue, mixing and master?). 

Maybe I've accidentally changed something in my settings. I don't know where I can change the function of this scrollbutton on my DDJ so far. So - if there should be a difference between the two settings, how do I regulate that in my settings? Or could it be that there is something wrong with my controller?

I hope you can help me. Thanks!