[SalesForce] Custom Setting issue in Test Class

I have written a pretty simple VF page that allows support users to add Case Assists (custom object related to Case) to their case. Pretty simple VF page, when opened, it creates a list of a wrapper class I created for users with a particular profile. Pretty simple SOQL query to grab all those users, and create wrapper objects off of them. After implemented, it seemed the support management team, was wanting to add and remove people outside of the support team at a somewhat often basis. This was a pain as I had hardcoded the SOQL query to look at the certain profile of the users. To solve this I created a custom setting that had a text field that held the user ID's of anyone to include in my SOQL query. This made it much easier as I could have an admin add and remove these people quickly without any coding changes.

Here are the pertinent pieces of my controller code

public with sharing class AddCaseAssistsController {

        private Case myCase;
        public list<userWrapper> uWraps         {get;set;}
        public boolean notTheOwner               {get;set;}

        public AddCaseAssistsController(ApexPages.StandardController stdController) {

            this.myCase = (Case)stdController.getRecord();
            myCase = [Select Id, CaseNumber, OwnerId From Case Where Id =: myCase.Id];

            uWraps = new list<userWrapper>();

            Support_Configuration__c supportConfig = Support_Configuration__c.getInstance();
            string userString = (supportConfig.Users_outside_of_support_for_assists__c == null) ? '' : supportConfig.Users_outside_of_support_for_assists__c;
            set<String> userIDs = new set<String>();
            userIDs.addAll(userString.split(';'));


            list<User> users = [Select Id, Name, FirstName, LastName 
                                From User 
                                Where isActive = true and (Id In: userIDs Or (Profile.Name = 'Imprivata Support' And Id !=: UserInfo.getUserId()))
                                Order By LastName, FirstName];

            for(User u : users){
                uWraps.add(new userWrapper(u, false));
            }

            notTheOwner = (myCase.OwnerId != UserInfo.getUserId()) ? true : false;

        }
}

This works fine and I can test it any which way in the UI and it works fine. The issue I am running into is when I write my test class. It seems that if I run my test method as myself (or just as the logged in user) it works fine and passes. The minute I try to use the RunAs() function in the test method, it fails and doesn't include any of the people whose IDs are listed in the custom setting.

Below works, but the minute I uncomment out the RUNAS() statement, it fails the assertion that the usermap includes the nonsupport user that is in the custom setting. The line below is what is failing, but only when i use the RunAs()

system.assertEquals(true, supportUserMap.containsKey(String.valueOf(nonSupportUser.Id)));

@isTest
private class AddCaseAssistsControllerTest {

    private static final Account acc = TestClassObjectUtility2.accountCreator('Test Account');
    private static final Contact con = TestClassObjectUtility2.contactCreator(acc.Id, 'Joe', 'Shmoe');
    public static final Id SupportCaseRT = Schema.SObjectType.Case.getRecordTypeInfosByName().get('Support Case').getRecordTypeId();
    public static final User supportCaseOwnerUser;
    public static final User supportNonCaseOwnerUser;
    public static final User nonSupportUser;
    public static Case myCase;
    public static final PageReference pg = Page.AddCaseAssists;
    public static ApexPages.StandardController stanCont;

    static{ 

        supportCaseOwnerUser = [Select Id, Name From User Where isActive = true And Profile.Name = 'Imprivata Support' limit 1];
        supportNonCaseOwnerUser = [Select Id, Name From User Where isActive = true And Profile.Name = 'Imprivata Support' And Id !=: supportCaseOwnerUser.Id limit 1];
        nonSupportUser = [Select Id, Name From User Where isActive = true And Profile.Name = 'Imprivata Sales Rep User' limit 1];

    }

    public static testmethod void NonSupportUserTest() {

            Support_Configuration__c supportConfig = Support_Configuration__c.getInstance();
            system.debug('Custom Setting Before: ' + supportConfig);
            supportConfig.Users_outside_of_support_for_assists__c = String.valueOf(nonSupportUser.Id);
            upsert supportConfig;

            myCase = TestClassObjectUtility2.CaseCreator(true, supportCaseOwnerUser.Id, acc.Id, con.Id, 'Email', 'New');
            stanCont = new ApexPages.standardController(myCase);

            //system.runAs(supportNonCaseOwnerUser){  **Uncommenting this makes it fail**
                Test.setCurrentPage(pg);
                AddCaseAssistsController controller = new AddCaseAssistsController(stanCont);

                Case c = controller.getCase();

                system.assertEquals(c.Id, myCase.Id);

                map<Id,User> supportUserMap = new map<Id,User>();
                for(AddCaseAssistsController.userWrapper uWrap : controller.uWraps){
                    supportUserMap.put(uwrap.u.Id, uWrap.u);
                }

                system.assertEquals(true, supportUserMap.containsKey(supportNonCaseOwnerUser.Id));
                system.assertEquals(true, supportUserMap.containsKey(supportCaseOwnerUser.Id));
                system.assertEquals(true, supportUserMap.containsKey(String.valueOf(nonSupportUser.Id)));
                system.assertEquals(true, supportUserMap.containsKey(c.OwnerId));
                system.assertEquals(true, controller.notTheOwner);
            //}

        }
}

This isn't necessarily a blocker as I can test this in the UI, logged in as any user and it works fine. I have used debug statement and the custom setting does get updated and include the user id, it just is not working when I use the RunAs() statement. This must be something to do with RunAS() and test methods specifically, I just can't find any documentation or blogs, or older posts that can answer why this is happening.

Any help or insight would be greatly appreciated.