When a PR is merged, the commit message is usually "{ticket_number}: {ticket_title}". If "ticket_number" happens to be a prefix of an existing Git hash in the repository, GitHub displays the ticket number as an hyperlink (see attachment).

Example: https://github.com/openjdk/jdk/commit/d19eab4f08592140229de43689c7d20ff7fbf4ee

Possible solutions to this problem could be enclosing "ticket_number" in backticks, or making it a proper markdown hyperlink to bugs.openjdk.org