I suspect that the issue you face has something to with stale values on the UI. The quickest way to check whether your settings are "sticky" is to open Internet options and going to Lan settings directly from control panel.
The following command will launch "internet options"
control inetcpl.cpl
Further if your machine belongs to some corporate domains, there might be group policies set by admins that periodically enforces some values for these parameters. In such cases, you might have to schedule a task for say every 10 minutes, and enforce values of your choice. (note: that is what I have been doing for quite some time)