Bootstrap 2.3.2: Thumbnail caption text wrapping to second line makes container height stretch

Question

I am looking for a way to display images with captions in a grid so all grid items are the same size. I am using the standard Bootstrap 2 thumbnails code as follows:

<div class="container imgGrid">
    <div class="row-fluid">
        <ul class="thumbnails">
            <li class="span3 center">
                <h4>Linked caption text</h4>
                <img ...>
            </li>

In this case, the extra "center" class centers the text. The imgGrid class sets the image size to width:100%, height:auto. This allows for different sized images to fit the grid since the widths vary a bit. Image height is not an issue in this case.

The problem is when the text caption is long enough to wrap to second line, the thumbnail container height increases and the grid is no longer symmetrical.

How can I make the extra text space cover the image rather than stretching the container height?