Selenium Switch To Method

new to selenium, take it easy on me :)

When i try to interact with a switched to page, the child page disappears and the parent page is brought back into focus. I have had a little google but am struggling to find a similar question.

public static void Initialize()
    {
        ChromeOptions chromeOptions = new ChromeOptions();
        chromeOptions.AddArgument("--start-maximized");

        Instance = new ChromeDriver(DRIVER_PATH, chromeOptions);
        Instance.Manage().Window.Maximize();
        TurnOnWait();
    }

IDriver is just a wrapper I use (have included initialise method for completeness).

public static void SwitchNextWindow(IWebElement windowOpener) {

        //Click the button that opens the new window
        windowOpener.Click();

        //Switch to new window
        string newWindowHandle = Instance.WindowHandles.Last();
        var newWindow = Instance.SwitchTo().Window(newWindowHandle);

        //This works
        newWindow.Manage().Window.Maximize();

        //The title is stored correctly but the window moves behind the parent
        string expectedNewWindowTitle = newWindow.Title;

        //This of course will not be found as we are now focused on the parent window
        var okButton = Instance.FindElement(By.Id("id_ok_submit"));

        //Parent page is shown at this point and errors out as element not found.
        okButton.Click();

        //If i manually bring the child page into focus (minimize parent) I can step over this code and it will find the button.
    }

//If i manually bring the child page into focus (minimise parent) I can step over this code and it will find the button.

//This happens for a find element call also and not just getting the title.

Many thanks guys.