Hi Bob,
It certainly looks like something is going wrong there. Rather than being an issue with stylesheets I think the image being pulled in from Facebook is simply of rather strange dimensions. Do you find this only happens with the theme you mentioned (ie are images imported as expected when you use a different theme)?
If you haven’t tried that out already could I ask that you do so (and, ideally, also deactivate all other plugins except for those by Modern Tribe) and check if Facebook event images import in the expected dimensions?
A workaround until our next release – which should be available soon and includes reworked code for pulling in images from Facebook – would be to manually remove or replace the featured images. I do realize that’s not ideal if you have lots of imported events to deal with, but it could tide you over until the next release arrives.
Let us know!