We tested the provided live url and noticed a problem with the height of the sliding pane in the browsers you mention. It seems that the pane's content div which comprises the sliding page has not been correctly resized. That is why, our suggestion is to try adding a style which sets height 100% to the RAD_SPLITTER_PANE_CONTENT_ctl00_darrpLeft. This is the only solution we can suggest you having only the live url.
In case the above suggestion cannot help you resolve the issue, please, send us a simple running test project which reproduces the problem so that we can test it on our side and take a closer look at your setup. Note that you will need to open a support ticket in order to have the right to attach files.
the Telerik team
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