This bug doesn’t happen in 4.4 or 4.5
Importing a (rigged?) object and changing a material in the details panel has the panel stop showing the rest of the materials in the list. Changing more materials doesn’t further shorten the list, so changing the last material when you first create the object “fixes” it. The missing materials still render, and they can be changed in the mesh editor, but the details panel seems to forget all about them.
This doesn’t seem to happen with every object, so I’m enclosing a simple 200k object that shows the bug. Create a new, empty blueprint project, import untitled.fbx (6.1 ASCII format), which is a rigged head with 3 materials. Change the middle material in the details panel and the last material is no longer shown in the list.
Editor: Version 4.6.0-2369412+++depot+UE4-Releases+4.6
(It would be real nice if I could copy + paste the version number from the About box, BTW)
Machine:
iMac (21.5-inch, Late 2013)
OS X Yosemite version 10.10.1 (14B25)
*2.9 GHz Intel Core i5
8 GB 1600 MHz DDR3
NVIDIA GeForce GT 750M 1024 MB