Explanation please? L2TP IPSec - effect of DHCP client options

Hi - I was tinkering with my configuration and managed to break my VPN server that I use to access my home network. I exported the two config files and found that the line that made the difference was this:

/ip dhcp-client
add comment="default configuration" dhcp-options=hostname,clientid disabled=no interface=ether1-gateway

which was changed in the broken config to this:

/ip dhcp-client
add comment="default configuration" dhcp-options=clientid,clientid disabled=no interface=ether1-gateway

Restoring the hostname option fixed the VPN.

Would anyone be able to explain exactly WHY this change affected my VPN server? Thanks in advance.