Create a mask, set Sample to Current Layer, click in Layer mask, sample
In other versions of Photoshop, when the Eyedropper tool's Sample is set to Current Layer, the Eyedropper selects the black and white values of the Mask. In Photoshop Beta, it's ignoring the mask and sampling from the masked image. This is undesired. Sometimes we have to paint the mask and color sampling makes this much easier.