Title has an equals method, that implements equality based on the interwiki prefix, the namespace, and the title text, ignoring the page ID as well as any fragments.
With Title implementing both the LinkTarget interface as well as the PageIdentity interface, the question arises how equality should be defined.
For LinkTarget, it would be natural to define equality to be based on interwiki prefix, namespace and title text as before, but include the fragment as well.
For PageIdentity, it makes more sense to focus on the page ID (along with the wiki ID), and only rely on namespace and title text if the page doesn't exist (and thus the page ID is 0).
All three notions result in the same behavior in most cases, but have different behavior in notable edge cases.
In order to resolve this, LinkTarget and PageIdentity should define distinct methods for determining equality, separate from the equals() method implemented by Title: LinkTarget::isSameLink() and PageIdentity::isSamePage().