How to stop new iPad backups from being encrypted?

It's Christmas and I have a new iPad Air 2. I plan to set it up as a new iPad using an existing AppleID and backup the iPad onto an existing Windows computer running the latest iTunes version.

Before I begin, I want to know how to ensure the backup doesn't become encrypted with a password I no longer know?

This is the third iPad owned over some time now, and the reason I ask this question is because some how the second iPad's backup became encrypted with a unknown password that was set on the first iPad. Unfortuatetly I thought I had solved this problem, but the tick in iTunes did eventually reappear. Refer previous discussion...

Where else is the "Encrypt iPad backup" setting stored?

Any suggestions would be greatly appreciated :-)

Regards, AjN3806