Applying a hover effect makes my images appear on same line not separate ..?

thanks for this plugin, its simple and nice.

I have 4 images , each appear under each other on separate lines.
When I apply one of your hover effects, WordPress re-arranges my page so the 4 images are now side by side on the same line.

When I take the hover effect off, it goes back to normal.

I can edit the html and put a <p> </p> and this works but it inserts an extra linespace which is not ideal. Any ideas?