How susceptive is an inductor to frequency and current?
In an air cored inductor this problems do not arise. It is the core material that introduces these seemingly bizarre dependencies. Take a look at 3C90 material: -



Fig1 shows how the real part of permeability peaks at a frequency of about 700kHz. In fig4 as flux density increases (caused by more current for example) the permeability also peaks up. Temperature has also an effect for many ferrites and fig2 shows how permeability is affected.

It's the core that causes these problems and the only resort is to use the manufacturer's data sheets if you can get them.