RichTextBox doesn't scroll on mouse wheel

Question

I have UserControl in SL4 project with a richtextbox with big amount of text in it. Problem that mouse scrolling doesn't work in it. While I dragging scroll bar - that works and when I press arrows on keyboard - scroll is working too, but when I am trying to use mouse wheel for scrolling - it doesnt work at all. I've reduced this control to simplest:

<UserControl x:Class="CTermsOfUsePage"
    mc:Ignorable="d"
    d:DesignHeight="800" d:DesignWidth="900">
        <RichTextBox  Height="400">
            <Paragraph>
              Big amount of text with many LineBreaks here.
            </Paragraph>
        </RichTextBox>
</UserControl>

But the scroll still doesn't work. I've tried to create a new SL application with such code - all is working fine there. I've also checked default styles - there is no style for RichTextBox.

Are there any suggestion - what can be a problem's source?

Update: problem occur in Chrome/FF/Opera in IE9 scroll is working fine.

Answer 1

We've found problem source. In project's .aspx file in <div id="silverlightControlHost"> section we have a setting <param name="windowless" value="true" /> . When this parameter has been set to false all worked fine.

As well as in IE "true" settings works fine it looks like SL bug.