strange mouse scroll behavior

[Andrea Zagli <azagli libero it>]

from a few days, on debian sid, i have a strange mouse wheel scroll behavior

it seems that is a problem of "gnome/gtk" applications, because it  
happens on epiphany but not on iceweasel, or in nautilus and in gedit  
but not in emacs

i try to explain: if a widget, with scroll bars, got the focus the  
next first scroll with the mouse wheel make the widget to scroll at  
the end of the page, and next scrolls work as expected

for example if i alt-tab to epiphany if i scroll it goes to the end of  
the web page; same thing if i right-click (it opens the popup menu so  
the main widget lost the focus) and then i scroll with the mouse wheel

it is a bug of my mouse or of gtk?

thanks in advance