There is a mistake in the SQL sentence used to filter the bugs in the changelog page. It's missing the project_id in the WHERE clause.
Here after the patched SQL sentence:
$query = "SELECT id, summary, view_state FROM $t_bug_table WHERE fixed_in_version='$c_version' and project_id='$f_project_id' ORDER BY last_updated DESC";
The result is that in the changelog of a specific project can appear bugs belonging to other projects.