See http://forum.openlaszlo.org/showthread.php?p=29450#post29450

Updated testcase:
<canvas>

<view width="300" height="300" clip="true">
<view bgcolor="red" width="300" height="800" id="se" onmouseover="this.ismouseover = true" onmouseout="this.ismouseover = false"/>
<scrollbar usemousewheel="true">

<method
event="onmousewheeldelta"
reference="LzKeys"
args="d">
<![CDATA[
if (se.ismouseover == true) {
this.step(-d);
}
]]>
</method>
</scrollbar>
</view>
</canvas>