The Ctrl+B and Ctrl+I shortcuts are assigned to the Bold and Italic browser's commands. You can use them in an editable HTML elements such as DIV and IFRAME.
My suggestion is to assign the Ctrl+B and Ctrl+I shortcuts to some other editor's buttons for example the Help dialog and Insert Time button, e.g.
<tool name="Help" shortcut="Ctrl+B"/>
<tool name="InsertTime" shortcut="Ctrl+I"/>
the Telerik team