Hey Simon,
I've just tested this out on a photo post with two comments (one from the original post, one from a reblog) via this request:
POST /v2/blog/{{blog-identifier}}/post/reblog
id={{id}}
reblog_key={{reblog_key}}
attach_reblog_tree=false
The created reblog post only has a photo and no text, as expected. Can you provide some more information about the requests you're making and the responses you're seeing to help us understand the issue you're having?
Regards,
Mike