EBay moved the dimensions lower on the Sell Your Item form. I've noticed that sometimes it will only ask for the weight of the parcel, sometimes all dimensions can be filled in, and sometimes it pushes me back to fill in the hxlxw. I just figure the gnomes running the program are on a cigarette break and don't let it annoy me. Not too much. Actually it does bug me since it slows me down.
Are you using metric measurements? That could make a difference.