$ _ SERVER ['http _ host'] An error occurred while obtaining the second-level domain name

$ _ SERVER [HTTP_HOST] an odd problem occurred when retrieving the second-level domain name. search engine Baidu

Use $ _ SERVER ['http _ host'] to obtain the HOST address.
I have A website A: www.nowphp.com
There is a second-level domain name: bbs.nowphp.com the post under this domain name is bbs.nowphp.com/1001.html
Question:
Baidu search engines sometimes include www.nowphp.com/1001.html
My website is divided into Chinese and English.
Sometimes, the host link address for sending the message will be replaced with www.nowphp.com/policy/101.html. it should be bbs.nowphp.com/policy/101.html.
I don't know why.

Reply to discussion (solution)

There are two types of domain name resolution: one is pointing to the ip address of a host, and the other is forwarding
The same is true for subdomains.

Most of your sub-domain names are forwarded instead of a dedicated host.

There are two types of domain name resolution: one is pointing to the ip address of a host, and the other is forwarding
The same is true for subdomains.

Most of your sub-domain names are forwarded instead of a dedicated host.
Thank you. it seems like you have some eyebrows. could you tell me in detail?

If the system paths of www and bbs are separated and then parsed in apache, the search engine should not be confused.

Or SEO filtering for search engine crawlers, which has not been studied.

Thank you, upstairs.
Additional questions:
I have A website A: http://www.nowphp.com
There is a second-level domain name: http://bbs.nowphp.com the post under this domain name is http://bbs.nowphp.com/1001.html