Fsx CRJ 700 ILS problem?

When using the CRJ 700 the glide slope needles are always on both in gps and nav mode. When I actually try to do a ILS landing the horizontal indicator will move and intercept but the vertical needle remains centers and the plane starts to sink. When I engage the ILS approach hold switch I am close enough to the runway that this should not be an issue. I also find it weird that it only stays in the center. Any help would be great.