Hi

Is that intentional or documented somewhere (I am running 5.16.2)?

I think perlop, yup, see http://perldoc.perl.org/perlop.html#Comma-Operator

It certainly violates the principle of least surprise for me but maybe there is a good reason for this behaviour...

Not sure about the source of the surprise for you , previous experience with X language or something :) but it is a common one, a fun thread about it at If you believe in Lists in Scalar Context, Clap your Hands