Order send_receipt=false is ignored, even though Storefront API is disabled

I was able to solve this. We were using custom app and access token instead of private app credentials. Storefront API permission affects custom apps also but the permission has to be disabled from another page. I went to partners.shopify.com and from apps menu opened our application. On the top there is App Setup and from there I disabled Storefront API. Send_receipt now works like it should.

Hope this helps anyone with the same problem.