Yeah great…. Thank you Microsoft!
In our scenario all WFE’s are connected to a SAN and therefore special network adapters are configured. After making some changes to the dns and removing the formely Crawl Webfrontend from the „productive“, user-accessible farm the search crawler replaced the hosts file with the IP from the Index server, but not the IP Adress from the public Lan but took the IP from the first SAN Lan Connection. Sounds complicated and strange….Imagine how the troubleshooting was…. 😦
Here you find a better explanation I hope…
But the greatest thing….
„Why might the entries be incorrect, you ask? Well, empirical tests show that the address selected by the process is the first address displayed on the first NIC displayed when you do an IPCONFIG /ALL. Also, there is one entry for each site listed in a crawl rule. Remove the site from the list and the HOSTS entry will magically disappear.“