Believe it or not but my customer forwarded an order-email where the template path hints of the single blocks are showing.
Nothing changed in config Path hints disabled Developer client IP set
It seems like it was only for this specific email. No other Emails affected.
Any suggestions would be much appreciated.
EDIT: To make it clear: It was an order email sent for an order created manually in admin panel which has different store view and therefore different settings where "display path hints" was true.