I have a 3-screen system with it set to act as one large screen. When I click the rename for a folder in LR CC, the dialog box comes up in the center monitor (where the original LR was running), but the LR window jumps to one of the side monitors. This happens at other times as well. It is not fatal, but definitely an annoyance.
I have two screens and something similar happens to me when I have Lightroom in Full Screen Mode. If I switch out of Full Screen Mode, it stays on the monitor I want. I'm wondering if you are experiencing this behavior while in full screen mode too?
No, it happens to me in either full or reduced mode. I still have LR5 on my computer and this does not happen with this version. This is really annoying!!