What is the difference ?

The vectirization (arrow over t) never is necessary and its confusing. use it only if you calculate with vectors, not with ranges!

t is a range, but Rows is a vector - thats the reason for the different answers.

A range is not a vector but kind of an implicit loop. It has 0 rows.

Its an undocumented trick that a range is turned into a vector if you use inline evaluation.

x:=1..5 is a range, but

y:=1..5= is a vector.

Here's a little image showing what Werner is talking about.

As you can see, using inline evaluation, T := t = [row vector] provides the results you desire.