Question for "rndc reconfig" on bind 9.11.4

[Techs-yama]

Hi, all.

Have a question for "rndc reconfig".

I tried to rndc reconfig option on 9.9.9-P5 and 9.11.4-P1 by source
installed binaries.

Behavior on 9.9.9-P5 was add new named.conf option and only add new
zone was loaded.

But, behavior on 9.11.4-P1 was add new named.conf option, add new zone
and existing zone reloaded.

Was "existing zone reloading" an assumed behavior in rndc reconfig on
BIND 9.11.4(or Higher version) ?

thanks.