Local Definition on lhs of definition carries over to rhs

Whilst thinking about Valery's request http://communities.ptc.com/message/187793#187793 , I had a little play with some indices and noted that a local definition on the left hand side of a worksheet definition (:=) seems to carry over to the right hand side.

I presume somebody's noticed this before ... works in M14..M15 and Mathcad Prime 1, but doesn't work in M11.

Stuart