Can't update table 'civicrm_contact' in stored function/trigger because it is already used by statement which invoked this stored function/trigger

I have a custom group that I edit to change which contact subtype can have it (removed a bunch, the list of like under is correct). Got the popup, clicked ok:

Can't update table 'civicrm_contact' in stored function/trigger because it is already used by statement which invoked this stored function/trigger

It seems to be CRM_Contact_BAO_ContactType->deleteCustomRowsOfSubtype

DELETE custom.*
FROM civicrm_value_klant_profiel_23 custom
INNER JOIN civicrm_contact ON civicrm_contact.id = custom.entity_id
WHERE (civicrm_contact.contact_sub_type LIKE '%
Medewerker
%' OR civicrm_contact.contact_sub_type LIKE '%
Partner_Medewerker
%' OR civicrm_contact.contact_sub_type LIKE '%
Pers_Medewerker
%' OR civicrm_contact.contact_sub_type LIKE '%
Leverancier_medewerker
%' OR civicrm_contact.contact_sub_type LIKE '%
Overheid_medewerker
%')

[nativecode=1442 ** Can't update table 'civicrm_contact' in stored function/trigger because it is already used by statement which invoked this stored function/trigger.]

I haven't been able to find which stored function/trigger is causing the trouble.