That does not sound normal to me. Do you zoom using the keyboard, or a mapped axis? Do you have a track demonstrating this behaviour? It might be worth asking about on forums.eagle.ru , as people there are more knowledgeable than I am, but I'll help if I can.
The world is going mad. Me? I'm doing fine!
Asus Sabertooth X58, i7 950 @4GHz, 6GB corsair Dominator 1600 MHz, EVGA GTX 570, Samsung 1Tb, 60 Gb OCZ Vertex 2E SSD