Does not work with NextGen galleries

I’m afraid I have never used NGG and I don’t have a fix for this. I think that it is an NGG issue which would also occur with other tab plugins so it is not something that can be worked around in the tabs plugin. The issue is likely to be that when the content is not visible on initial page load, the size is ignored when it is shown. The fix would need to be NGG specific and might involve the gallery content being reloaded once it becomes visible.