Landing to the south at DFW in an MD80 one day with 1000 and 3 we were cleared for the ILS and the FO started a steep descent exceeding 1,000 FPM. The glide slope was pegged full down and we were in the clouds. Looking at the DME at the runway end and our altitude knew we were not high so told him to level off, the glide slope was wrong. 20 seconds later the glide slope snapped to showing us low.
I advised the tower of what happened and they said we don't have to protect the glide slope if the weather is better than 700 and 2. I said we were coupled so does that mean in the future we should only do the localizer approach since the glide slope can't be trusted? He said an aircraft crossed the ILS protected area because of the adequate weather. We didn't get below 1500 ft but it made me closely monitor what the ILS is telling you and if it is real or not.