"Can any anyone explain whats happening"
That is the behaviour of matlab since R2016b introduced implicit expansion. If you want element wise addition of the vector elements make sure your vectors are in the same direction. What you see now is equivalent to
bsxfun(@plus, A, B)
in versions prior to R2016b.
Much has been written about implicit expansion. No point complaining about it, it's not going to change. In my opinion, your operation should have been an error in <R2016b.
