Hi,
You must be using an old version of LightMart, this problem has been fixed already.
This has nothing to do with user being logged-in or logged-out. It is a jQuery issue caused either by cache or visitor temp. internet files. jQuery calculates the product picture height wrongly and this wrong calculation leads the layout problem.
The solution is quite easy.
Open this JS file:
/template/flexible_lightmart/js/template.js
Look for these lines:
var ProductDetailsFixheight = $('#vmFlyPageTop').height();
$('#vmFlyPageTop').css("height",ProductDetailsFixheight);
remove them completely.
The problem will be gone.
Regards.
Support & Development