You're getting what are called "blown-out" highlights, meaning that the highlights are so bright that they have no information in them at all, meaning that there are areas that are absolute white. Digital cameras are notorious for blowing out highlights, more so than normal film, because the sensitivities of chips are more than normal film, and they expose differently(a very typical example is someone taking a picture of a subject next to an open window. the subject is very dark and the light from the window is a blob of blown out highlights. this can be remedied by using fill flash if your camera supports that, or just turning the flash on). Sometimes however, you can rescue parts of your image that look blown out, but are not actually tone-less. The way you can do that is simply do a curves adjustment layer, and pull the curve all the way down as far as you can. This will be the test to see if your highlights are in fact absolute white. If you find that there is tonal information in your highlights, you can keep that curves adjustment layer on the darkness level that you would like your highlights to be. Then mask out normal parts of the image so that they arent affected by the darkening of the adjustment layer. Hope this helps.