Are there any recipe ingredients that scale in a non-uniform manner?
Things applied in a non-linear manner do not scale linearly, i.e. when the 'Surface to volume ratio' matters, the recipe will not scale linearly.
See  http://kitchenscience.sci-toys.com/scaling for a discussion mostly on how the timings are affected.

One example is breading: You will not need to double the breading linearly on a single 200g piece of beef/chicken compared to a single 400g piece, since the surface area will not change with the same factor as the weight, i.e. the surface area will not double when the weight doubles. 

On the other hand, if you use twice as many pieces of chicken, you will need twice as much breading.