GtkAjustements strange behaviors ? (gtk 1.2.10)

[Paul Cheyrou <Paul Cheyrou-Lagreze inrialpes fr>]

I've noticed two strange behaviour on a gtkadjustement that we use in the development of GTK-Amaya ( 
http://www.w3c.org/amaya/ ) :

1. When I get y mouse postion on a vertical scrollbar, specially on the lower button, I often (not always, 
altough i clicked in the same place) get a small y mouse position... Shouldn't it be always a big y or it is 
normal ?
(on a mouse callback registered on the window)

2. When I click on the buttons up or down, it doesn't give the same step each time. ie : I give a 
step_increment of 6 and I get a step of 7,9,12...
Is this normal ? 
How can I detect a user click on those button if step isn't the same each time ? Is there another Way ?

Can someone confirm or infirm those statements ?

Tk