Unity 2017.3.0p1 Model Import - Can't Set Material Name & Search Options

This has only just started happening, but when we try to import new FBX models into our project, and either use Remapped Materials or External Materials, we can't set the material Naming or Search parameters to anything other than "From Model's Material" and "Project Wide" respectively. Whenever we try to change them, these parameters are REVERTED when we hit 'Apply'.

This could seriously affect our workflow, because if we can't name a model's materials with the model name prefix, or isolate those materials to the model's local folder, we may inadvertently change materials that are used by other models in other scenes.

Has anybody else encountered this issue?