Just re-built from github - it's behaving differently, but not working quite yet. It used to release the modifier key on any mouse event (not just scroll), which it doesn't do any more. Unfortunately, there seems to be something else going on - the OS still doesn't recognise the ctrl+scroll command to zoom, which works when the driver is disabled.
I noticed something else after re-building - on the "K95 RGB", "Device" tab there is a button next to Status that reads "Up to date", clicking it tells me that there is a firmware update available, but that I need a new version of ckb. Possible bug, as I've only just downloaded the latest version.