It is not required to have RadScriptManager on the page when enabling RadCompression.
Does replacing the ToolkitScriptManager is asp ScriptManager or setting its CombineScripts
property to false/LoadScriptsBeforeUI
to true produce different result? There is also an issue with the Sys.Application ScriptLoader (when LoadScriptsBeforeUI is set to false) mentioned in this forum thread
which might be somehow related to this matter.
the Telerik team