I've been trying to trace through the code to answer this myself - and I have to cry uncle...
What is triggering the decision to use
/etc/imscp/bind/parts/db_e.tpl
rather than
/etc/imscp/bind/parts/db_master_e.tpl
I'm going to update 1 (or both templates perhaps - depends on the response :D) to refer to 2 slave NS's that I've set up - but I want to make sure I've caught all the locations that the system will use to throw the NS names in.
My testing thus far has produced .db files with 3 name servers defined in them - and I want to make sure only the 2 slaves are there.