title: Nuget package source is unchecked automatically
body: <p>I have added our org specific <a href="/questions/tagged/nuget" class="post-tag" title="show questions tagged &#39;nuget&#39;" rel="tag">nuget</a> package sources that has urls pointing to our local network for which I have complete access. After adding it by checking the checkbox in the package manager settings and closing the window, when I check the list of package sources again, one specific package source is getting removed ("unchecked") automatically. Either <a href="/questions/tagged/visualstudio" class="post-tag" title="show questions tagged &#39;visualstudio&#39;" rel="tag">visualstudio</a> or <a href="/questions/tagged/nuget" class="post-tag" title="show questions tagged &#39;nuget&#39;" rel="tag">nuget</a> extension removes the source.  The same source was working sometime back. Not sure if it has anything to do with VS/OS updates. At the same time, other custom package sources are working and other team members are not facing this issue.   </p>