There are two opposite situations. One is when several things are viewed as one thing while they're actually different (too much abstraction), and another, where a thing is viewed as different things, when it's actually a single one (when code is just copied over).

In my experience, the best way to solve this is to better analyse and understand the requirements. Do these two pieces of code look the same because they actually mean thing in the meaning of the product? Or they just happen to look the same at this particular moment in time, and can continue to develop in completely different directions as the product grows?