We can not guarantee compatibility with custom themes. You would have to remap the vbgallery style settings to match that custom theme or maybe add into your new theme any missing style elements from the default style.
I would suggest you check out your page source look at the style classes and how things render in the default style then see how things are in the custom style and see what is missing in your custom style and you will resolve your issue.
Likewise using vbGallery on the latest vb
you could have style issues since technically the latest vbulletin vbgallery 3.01 would support without any issues would be 4.1.1