I fixed this by writing my on Razor Template for the Gallery Browser.  I did not use your macro and I added a property for Gallery Thumbnail to make it easier to select the image.  The other alternative would be to select the first child of the Gallery Object.  I opted not to do this.  Here is the code from my template:

@foreach (var page in @CurrentPage.Children())

{

<div class="GalleryBrowserContainer">

<div class="GalleryItem">

<div class="GalleryThumbContainer">

<a class="GalleryThumbLink frame" href="@page.Url">

<span class="GalleryThumb" style="background-image: url(/[email protected](page.GetPropertyValue<string>("galleryThumbnail")).umbracoFile&width=240)" title="@page.Name">@page.Name</span>

</a>

</div>

<div class="GalleryTitleContainer">

<a class="GalleryTitleLink" href="@page.Url">

@page.Name

</a>

</div>

</div>

</div>

}

Here is a screenshot of the result:

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