Workaround: add addinstance capability in db/access.php , e.g.

'mod/tab:addinstance' => array(
'riskbitmask' => RISK_XSS,

'captype' => 'write',
'contextlevel' => CONTEXT_COURSE,
'archetypes' => array(
'editingteacher' => CAP_ALLOW,
'manager' => CAP_ALLOW
),
'clonepermissionsfrom' => 'moodle/course:manageactivities'
),