Random gaps appearing for horizontal slide effect

When viewing a slide of images using the horizontal slide effect in a block, there's a tiny gap appearing between images during the slide effect and it happens randomly, not every single time.

Most of the time, it looks like a 2-3px gap and sometimes it looks wider like 7px.

It's happening on all browsers I've tested on: Chrome, Firefox, Safari. I'm running the default version of jQuery (1.4.4) that came with Drupal 7.