Keyboard issues with KVM USB passthrough

I've got an interesting issue going. A few months back, I set up my PCI passthrough build to run Windows 10 on a Linux host using KVM. Everything was dandy, but I had some trouble with passing through USBs back then, and I just sort of gave up eventually and worked around the problem.

Well, I recently started fooling with it again, and I managed to pass through an entire USB controller, which is great, I can plug-and-play devices on the fly, but I've got just one odd issue. My keyboard is one of the USB devices being passed through (a Das Keyboard Model S), and when passed through, it works fine, except the caps lock, num lock, and maybe scroll lock are acting up. If I turn them on, they will come on, and work just find for about 5 seconds, but then turn themselves right back off! It's the darnedest thing and I just don't' know what's going on. Any ideas?