When configuring a host for IPMI via the web frontend, the host entry will lose its DNS name configuration. The DNS name displayed on the "Hosts" overview in configuration will become the IPMI device name.

Prerequisites:

• Existing host without IPMI configuration
• Both, DNS and IP address configuration items are filled out
• "Connect to" is set "IP address"

To reproduce:

• Chose to configure an existing host with no IPMI configuration yet
• Tick "Use IPMI"
• Enter the IP address of the IPMI device, IPMI privilege level "Admin"
• Use IPMI authentication algorithm "straight" (not tested with others) and fill in IPMI username and password
• Save the host's configuration

You will be redirected to the host configuration page. Notice how the column "DNS" has changed to the IP address that you entered in the IPMI configuration.
Click on the host again to edit it. Notice how the DNS configuration item is blank.

What I also noticed is, that once you change the "DNS" configuration for the host back from blank to the previous value, the ZABBIX server will try to use the DNS configuration value now for connecting to the IPMI device.

I haven't had a chance to test whether this occurs in any later version, but I have not seen any IPMI related items in the Changelogs.
Please have a look into this issue. Thank You.