When the LocalDb is window is open the first time it can download a localdb material to the active octane material. This works the first time. Now select a new object with a new octane material. Make a new download from the localdb and still goes to previous selected material, not the current selected material.
The only way to download localdb materials to new octane material after the first time is to close the localdb window and reopen it for every new octane material.
I have tested with 4.01.1 - 16.3.1 and 2018.1 - 17.0. Under Windows and Nvidia rtx2070 with the latest driver.