It looks like that somehow on initial map loading and just after 
tilesloaded event the map hijacks mouse focus without user clicking on the 
map or the hosting div element.
Result is that if the user happens to play with his mouse wheel at the time 
a burst of unintended unpleasant zooms are fired.
This has been only been observed in Firefox   V.3.0.13 while this dos not 
happen when I checked with Chrome V 4.0.203.2

Temporary work around seems to be: 
Create the map with option {scrollwheel: false} thus disabling it initially 
then re enabling it after first onmouseover event xxMapObject.setOptions 
({scrollwheel: true})} 

A page exhibiting this behavior and source code can be available upon 
request.