SharePoint 2010 - FAST Search Document Preview Did Not Show Up

I also discovered the followings:

1. If I do server name mappings in sharepoint central admin to https://intranet.acme.com/ then when I perform the search, here is what happened

a. link to the document in result search page pointed to https://intranet.acme.com/

b. link to "view in browser" point to

c. No document thumbnail

2. If I removed the servername mapping

a. link to the document in result search page pointed to

b. link to "view in browser" point to https://intranet.acme.com/

c. Document thumbnail display OK

I don't know if there is a bug in FAST search, we are only get the document thumbnail if we remove the server name mapping and content source point to crawl server . However, this is not secure since we want both the link to the document point to https://intranet.acme.com/ not .

Regards,