Lambda@Edge for "origin request" doesn't receive custom headers

I have a CloudFront distribution with S3 origins. In the origin settings there are custom headers added (i.e. "x-test"). The behaviour has two Lambdas: for "origin request" and "origin response" hooks (both NodeJS). It is all completely fine with the one for "origin response" hook, but the one for "origin request" doesn't receive "x-test" header in the event...headers object. All the docs and articles I've read say that "origin request" Lambda should get this header too. Tried to add "x-test" header to whitelist in attached "origin request policy" - this didn't help. Cannot find ANY information why could this happen. Does anyone have any ideas?