Under windows only one software can connect to a midi device. So indeed if Minibrute Connection is connected, then Reaper can open the Midi device. But the opposite is true too: If reaper is connected, Minibrute Connection will fail to connect. It one of the strong limitation of Windows Midi driver.
I'm very surprised connecting an other USB device could disconnect the Brute. unfortunately I don't have Novation XIOSynth or Korg NanoKontrol, but I'll check with other Korg and novation devices. But are you sure the disconnection is not related to a software you may have launch while plugging theses devices, such as reaper? I could be this windows driver thing too.
If you have some spare time to investigate I would be very grateful