Users expect content to react predictably and have an understanding of how certain content types work. Deviating from this predictably creates accessibility issues for all users, especially those with certain disabilities.
To avoid these issues, make sure all your content behaves in a manner typical to the content type and does not trigger new windows, move focus or rearrange content without warning or prior indication. If an assistive device moves focus to a block of content, it should not trigger an automatic change unless the user is informed before using or accessing the content.