Well - I had the Faderport installed on a system with 8.5 on it. Then I installed X1, and the Faderport would not work nicely with X1. What I did was completely remove the drivers (even cleaned up the registry using regedit), and then installed them again. That did the trick. Everything worked as expected.
At this time I am using a dual-boot system with 8.5 on one partition and X1 on the second one (well actually I have more partitions in use, but they are for Linux - wont bother you with that). As I am increasingly using only X1 I think I am going to erase the "8.5 partition" within a little while. I just wait for the X1b update and if this addresses the latest small niggles I have it is the end of that partition... but enough of that..
On the clean install the Faderport works exactly as expected. All buttons are behaving the same as in 8.5. Be sure to use the Faderport control surface entry on the setup, and the "USB Devices" as in- and output. If you have more than one controller make sure the Faderport is the last one. I also use the E-MU Xboard61 (nice cheap MIDI Keyboard with aftertouch and rotating controllers) and noticed when the Faderport was on top weird things where happening - don't ask why I really don't know.
Hope this helps a little..