I have my events window set to the second display and my viewers on my main display. The main display is a 27 inch Thunderbolt, and my second display is a legacy Cinema HD display going Thunderbolt to DVI adapter to Display.
When I startup Final Cut X, the menu correctly shows that my events should be on second display and my viewers on the main display, however my events show up on top of my viewer window, both on the main display.
If I toggle the settings in the menu it reverts to the correct setup, but it's an annoying bug that I can't seem to get rid of. Any ideas?
Sounds like you're using the Mavericks display mode where each display is a space with a finder bar across the top. It just doesn't work with X. It does to a point as you're finding, but switching spaces, restarting, swapping settings, etc will have strange results. I have the same setup as you and I was excited about this new feature in Mavericks, but I soon turned it off after seeing the same issues.
Maybe they'll fix spaces with Yosemite. Seems like I've been hoping they'll fix spaces since Lion. I thought Mavericks was the fix, with separate spaces for each screen. Oddly it seems it works for non-apple apps. But Motion, FCP X and apps that have this weird non-windowed "show on second display" type mode seems to break the concept.