iMessage disable from iPad but not iPhone

Hi all,

This issue has come to light today.

I am running an iPad Air2 and an iPhone 5S both running 9.3.1 - (13E238).

I have been using iMessages for ages on the iPhone, and off on iPad (no need for all messages in both places), but today, I can not get access to my SMS messages on the iPad without signing in to iMessages... When I sign out again in Settings for the purpose of only getting SMS messages on the iPad, the system demands iMessages again, without an option to decline.

Any thoughts anyone?