What I believe that will be the easiest way to resolve the issue is the following:
1) Temporary remove the entire parent splitter from your page and set a DIV element with some background color on its place and apply the same resize logic to it - you should get the very same result as with the splitters.
2) Resolve the problem with the DIV element and make it work as you require.
3) Replace the DIV back with the splitters definition and apply the same logic as with the DIV and you should get the desired result.
In case you need further assistance with this, please open a new support ticket and send us a small reproduction demo which is fully runnable along with detailed explanations and some screenshots of the actual and the desired result and we will do our best to help.
the Telerik team
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