It seems the theme stylesheet sets the float property of the gallery item to left, which is causing the flow issue. We will add an override in the next release of RPS Image Gallery, but until then you can set an override using the following CSS.
`.gallery .gallery-item { float: none !important; }’
Perhaps you already have the ability to override your theme’s CSS directly, but if not, you may want to use a plugin which affords this capability through the WordPress administration screens. Jetpack, a plugin by WordPress.com, features a Custom CSS module that should do the trick.
We did check the gallery view in the latest versions of Firefox and Internet Explorer and the captions do seem to be centering. There is an inline style associated with the gallery-caption element which specifies text alignment is to be centered and it is unlikely that anything is overriding the value. However, if you are still seeing the caption centering issue after applying the float override, please let us know so we may address it. Thank you.