I bought a G600 Logitech mouse specifically for MWO (loved the idea of putting my arty/airstrike on thumb buttons).
I downloaded the software and rebound the buttons to my delight, reassigning DPI up/down, changing the G-shift button into a third mouse button for Weapon Group 3, etc. Some significant rebindings, but everything allowable.
However once I open the game, Windows fails to recognize my keyboard. I can't even type in my password to the game--when I type I get the "device disconnected" soundbyte from Windows. Windows seems to recognize the mouse button keybindings as a secondary keyboard which supercedes my actual keyboard. (before opening the game I can open Notepad and type using both the mouse and my keyboard; after opening and closing a game, I can only type using the mouse--I have to restart my computer to use my keyboard)
I tested this out with both MWO and Dota 2 and I have the issue in both games, so it's not a MWO problem, and I tried it with both MWO Steam client and the "classic" client (which I have perma-set to 32-bit to avoid DirectX issues), so it's not Steam.
I found that if I did a complete reset and uninstalled (and didn't reinstall) the Logitech software and didn't press any "special" buttons on the mouse I was able to use my keyboard, but then all I had was an expensive 4-button mouse with a bunch of useless and potentially very dangerous buttons

Changing the version of the software didn't help (a friend encountered something similar and fixed it by going back a couple versions). I can't recall if I ever tried downgrading to 32-bit from 64-bit--I doubt it since I'm running 64-bit Windows 10 and 64-bit MWO.
I ended up returning the G600 for a G700S, and not surprisingly encountered the EXACT same problem.
I sent the issue to Logitech and they were not helpful. Since MWO players seem to be a very helpful lot I figured I'd try my luck and see if you'd seen it.
Other details: Running Windows 10 64-bit; my computer is less than 2 months old, an iBuyPower I got from NewEgg.