I already answered your support ticket with the same question. I will give the information here as well, so that it is available to all, who might run into the same problem:
The problem is caused from the FullScreenMode property that you
have applied to your main RadSplitter:
|<telerik:RadSplitter ID="MainSplitter" runat="server"
| FullScreenMode="true" Orientation="Vertical"
| VisibleDuringInit="false" Height="100%">
As soon as you remove this property, you will get the expected result.
You have configured your page correctly for the RadSplitter to occupy
100% of the height of its parent and removing this property would not
change the layout of the page. You should just add Width=100% to get the effect of the FullScreenMode.
Yes, we did change the implementation of the VisibleDuringInit property
for performance reasons. Now, when you have a lot of HTML in the
RadPanes and VisibleDuringInit=false, the RadSplitter loads notably
faster. However, the new implementation does not work as expected when
you set FullScreenMode=true.
The FullScreenMode property was introduced so that you can configure
the splitter to become as high and as wide as the browser window when
the splitter is a direct child of the FORM element and without the
necessity to set the splitter's Width and Height properties and the
Height of the HTML, BODY and FORM elements. However, it works only in
few cases as people expect it to. That is why we decided to change the
implementation of the VisibleDuringInit property and mark the
FullScreenMode property as obsolete (we will do this for the next
update of the suite).
the Telerik team
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