Help me out here

I’ve been using photoshop for quite some time now, and today I ran into a problem I’ve never experienced before. Maybe you guys can help me out.

Go into photoshop, create a new layer. On that layer make any shape you want. Apply a drop shadow to the shape through layer styles. After you have applied the drop shadow, add a layer mask, once you have done that, use the gradient tool to mask out some of the shape.

Now… my problem is, when I do this, the layer mask is actually apply a gradient and a mask to my shape. I have no idea why it’s doing this, I’ve used this technique thousands of times and never have had this happen. I reset my photoshop defaults and everything… i’m stumped.

Here is an attachment of my result, hopefully my instructions were easily understandable.