Site collection admin with full control does not have ManageWeb permissions?

Question

I have a user set up as a site collection admin at the root level of my sharepoint site, and all subsites inherit these permissions. I have also verified that my user admin1 has FULL CONTROL rights to the entire site...so why do both IsUserAdmin and ManageWeb permissions return false??

If I run this code against my global tenant admin user, both values return true. What gives? I do not believe the App-only policy applies here.

using (
    var ctx = TokenHelper.GetClientContextWithAccessToken(
        webUrl, sharePointAuthResult.AccessToken))
{
    var spWeb = ctx.Web;
    var user = ctx.Web.EnsureUser(accessInfo.UserEmail);
    ctx.Load(spWeb, w => w.EffectiveBasePermissions);
    ctx.Load(user);
    ctx.ExecuteQuery();

    var managePermission = new Permission(
        "Manage",               
        ctx.Web.EffectiveBasePermissions.Has(PermissionKind.ManageWeb));

    var isAdmin = user.IsSiteAdmin;

    /*

        managePermission.IsGranted == false    (why?)
        isAdmin                    == false    (why?)

    */
}

In case it's useful, I am developing an Office 365 snap-in app for Word, so I am using the OAuth2 Authorization Code Grant Flow to allow the user to grant consent to the app for read / write permissions.

Answer 1

A related answer was posted here by Vadim Gremyachev. It turns out checking the IsSiteAdmin property on the current user object directly isn't a reliable result; instead, checking for the property on Site.RootWeb.SiteUserInfoList was a reliable approach for me.

CurrentUser.IsSiteAdmin should be true but returns false

Another way to determine whether user is site collection administrator Supported in SharePoint 2010/2013

public static bool IsUserSiteAdmin(ClientContext ctx,int userId)
{
   var userInfoList = ctx.Site.RootWeb.SiteUserInfoList;
   var item = userInfoList.GetItemById(userId);
   ctx.Load(item);
   ctx.ExecuteQuery();
   return (bool)item["IsSiteAdmin"];
}                  

Usage

using (var ctx = new ClientContext(url))
{ 
    var currentUser = ctx.Web.CurrentUser;
    ctx.Load(currentUser);
    ctx.ExecuteQuery();

    var isCurrentUserSiteAdmin = IsUserSiteAdmin(ctx, currentUser.Id);
}