Hi,
I was trying to set and save download quotas. (no need for upload) If I was shutting down the internet, it worked okay. If I was trying to throttle instead, it wasn't saving. It said everything was fine, but the throttle values were not saved. Hmm.
I poked and prodded and pondered for a while with default and new qos classes before it occurred to me to enable upload qos. This worked.
With upload QOS enabled, I was able to edit and save and everything appears to be okay. I'm still only using download quotas, but upload qos has to be turned on too.