In 3.2.1, for a moderator to have an option to mass soft delete posts from MCP this moderator has to have a hard delete permission. Meanwhile, soft delete of each post separately (from the topic itself, not from the MCP) works fine even if the same moderator has no hard delete permissions.

In other words, a moderator can (soft) delete posts from a topic by clicking a delete button on each posts, but they cannot bunch (soft) delete many posts at once from MCP of this topic.
 
Suggested fix: in includes/mcp/mcp_topics.php find:

        'S_CAN_DELETE'        => ($auth->acl_get('m_delete', $topic_info['forum_id'])) ? true : false,

replace with

        'S_CAN_DELETE'        => ($auth->acl_get('m_softdelete', $topic_info['forum_id'])) ? true : false,