The width of the div should be set to the thumbnail width by default.. Do you perhaps have some other css in your site template that is messing it up?
In gallerypicturetpl there is:
<p style="width: [+maxigallery.picture_width_thumb+]px;">
[+maxigallery.picture.title:htmlent+]
</p>
And the width to that placeholder is taken via
getimagesize. Is the width value wrong if you check it from the html source of the rendered page?
"He can have a lollipop any time he wants to. That's what it means to be a programmer."
No, it’s in the template /assets/snippets/maxigallery/templates/gallerypicturetpl.html
"He can have a lollipop any time he wants to. That's what it means to be a programmer."