Yeah, ok there may be some uses like yours (which I would consider a hack), but in general (at least that would be the behaviour of least surprise) you (ok: I) would expect that when you run a script as "a.pl" you get your command-line flags from the shebang-line and when you run it as "perl <whatever flags> a.pl" your get it from - well - the command line.

With this behaviour I cannot run a script with different flags without having to modify it if it contains a shebang lines with flags.

Do Python and Ruby do this as well?