[web2py] Function is evaluated twice?

[Serbitar]

I have the controller:

@auth.requires_login()
def roll():
    if request.args(0):
        step = int(request.args(0))
    else:
        return dict(message = "Roll it!")
    if request.args(1):
        visible = False
    else:
        visible = True
    result = util.roll_step(step)
    db.live.insert(username=auth.user.username, value=result,
step=step, visible=visible)
    return dict(message = result)

the util.step function just generates some random numbers.

when I call:

application/controller/roll/5

the roll() function inserts ONE entry into the db with visible is True
(just like intended)

when I call:

application/controller/roll/5/1

or

application/controller/roll/10/3/10

or

application/controller/roll/7/whatever

the function inserts TWO entries into the db (with visible = False,
like intended). Why does it insert two?

Thanks in advance.