Virtual Sites - Taxonomy page reverts to default theme

I've set up several sites using Virtual site, each with their own theme - everything is working fine except the taxonomy term pages, which display using the default theme.

Each virtual site has the same issue - whenever I click on a taxonomy term, the term page is in the default theme. I've cleared the cache, resaved the view, rescanned templates etc an nothing seems to work.

Can you please help? What is it about the taxonomy page e.g. http://example.com/taxonomy/term/123 that is bypassing the virtual site theme?

Thanks