Because of operator precedence, + has more priority than :. Therefore your expression is equivalent to :
1 : (4 + A(:)')
which is
1 : ([5; 4; 4; 5])
Because of the colon rule, only the first element of a vector is considered, the above is thus equivalent to:
1 : 5
I suspect you may have wanted
(1:4) + A(:)'
which will result in a 1x4 vector pre-R2016b (or it may error, I can't remember) and in a 4x4 matrix in R2016b or later.
