[Plugin: NextGEN Gallery] Thumbnails changing lines

Hey, I have been working on a site obviously using nextgen gallery. When my client adds new images to the gallery page sometimes one of the thumbnails will skip to a new line instead of being in a 4 across grid like it’s set to in the configurations. The HTML is unchanged and I can’t figure out why some of the images do this. To try and fix this problem, I have re-created the thumbnail from the backend that is before when the images jump to a new line and this seems to fix the problem on most occasions.

Has anyone had this problem before at all? Is there a way to fix this or any idea of what the cause is?

Any help would be great.

Thanks