Try playing with some of the code in postformat.php. As an experiment I just tried renaming the post-thumb and thumb-shadow classes like the following line.

<?php bfa_thumb( 620, 180, true, '<div class="thumb-shado"><div class="post-thum">', '</div></div>' ); ?>

That took out all the effects. Just renaming the thumb-shadow class left the fade in but took out the shadow.

This is the kind of playing around this theme makes easy as you can make changes to a virtual file and then hit the, in this case, subtemplate-postformat button on the bottom to revert to default state if you don't like the results or made a mistake.

Just take the thumb-shadow div out altogether. If the grayscale image is gone, then there shouldn't be any animation between the two images.

In postformat.php, change this:

<?php bfa_thumb( 620, 180, true, '<div class="thumb-shadow"><div class="post-thumb">', '</div></div>' ); ?>

to this:

<?php bfa_thumb( 620, 180, true, '<div class="post-thumb">', '</div>' ); ?>