Using a variable in a loop before it is defined?

Whilst looking at another worksheet in Mathcad Prime 10, I noticed that an as-yet undefined variable in a loop had a value (albeit zero)

I can't remember if this was standard behaviour in previous versions of Mathcad or not.   However, it certainly caused me some moments of pondering whilst I tried to determine how a variable was initialized in a much longer program (that I was trying to understand in the first place!).

Stuart