oembed links not working

By default, WordPress includes 2 oembed headers:
<link rel=”alternate” type=”application/json+oembed” AND <link rel=”alternate” type=”text/xml+oembed”

When custom-permalinks is activated, the address is correctly replaced in the header.
However, when opening the included oembed links, a json oembed_invalid_url 404 response is generated.
However, when opening the oembed address with the original URL, the response is correctly generated.

Example to reproduce:
original address: http://www.host.com/mycategory/mypost
custom permalink address: http://www.host.com/ThiIsMyPost

generated oembed in page headers:
<link rel=”alternate” type=”application/json+oembed” href=”http://www.host.com/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fwww.host.com%2Fmycategory%2Fmypost”&gt;
<link rel=”alternate” type=”text/xml+oembed” href=”http://www.host.com/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fwww.host.com%2Fmycategory%2Fmypost&format=xml”&gt;

result from http://www.host.com/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fwww.host.com%2Fmycategory%2Fmypost:
{“code”:”oembed_invalid_url”,”message”:”Not Found”,”data”:{“status”:404}}

result from the original address with custom permalinks activated
http://www.host.com/wp-json/oembed/1.0/embed?url=http%3A%2F%2Fwww.host.com%2Fmycategory%2Fmypost:
{“version”:”1.0″,”provider_name”:”host.com”,”provider_url”:” ……….–remaining content removed–