Each migrated question has a notice like the following attached:
migrated from biology.stackexchange.com Nov 29 at 14:22
This question came from our site for biology researchers, academics, and students.
This notice links to a revision of the source question. But it should actually link to the question itself with the URL parameter that prevents redirection. As it is now, anyone not a moderator on the source site can't actually get to the original question without manually manipulating the URL. Following the link from the revision page triggers the redirection to the site where the question was migrated to.
The migration notice should not link to a specific revision, but to the main question in a way that doesn't trigger the redirect. As far as I remember that was the original behaviour, and I assume this was changed accidentally.