question on scatter

Hello,

I did a mistake with scatter function and I remark a strange things.
The size change even when I pass a bad argument. It's seems that the default size change if the size is equal to None or to something stupid. It's not important but I prefere to tell you this comportment.

M = 30
x = (rand(M)*scale-scale/2) * .4
y = (rand(M)*scale-scale/2) * .4

scatter (x,y)

M = 30
x = (rand(M)*scale-scale/2) * .4
y = (rand(M)*scale-scale/2) * .4
scatter (x,y,s='s')

N.