Hi, problem with quick tasks is that we put verification steps there and the action steps are supposed to be recorded. In this particular case it really makes sense to have those specific steps in quick tasks, we'll discuss it.
Meanwhile there is a second option for adding such steps, you can simply click on the RadMenuItem and this should record RadMenu('ctl00_ContentPlaceHolder1_RadMenu1'): item '' action -> 'Click' step and you just have to change the action to "Open" instead of "Click". Actually that's the initial reason why we have verifications in quick tasks because the idea is to record actions and then choose the verifications from the verification builder or quick tasks. Obviously this have its shortcomings, this case is an example. We'll try to think of a more convenient way to expose the available actions for specific controls, at the moment it is done through step suggestions only.

On the third part of your comment, by using this actions you shouldn't need to verify if the menu item is visible. 

When you record a test for RadMenu, you should use the "open" action. The step default description is RadMenu('ctl00_ContentPlaceHolder1_RadMenu1'): item '' action -> 'Open' you can create this kind of step using step suggestions, select the element which is the RadMenu, click on "Step Suggestions" and select the "open" action. 
In code the step should look like this Pages.TelerikSASPNETMenu.ListItem.Open(); where ListItem is the RadMenuItem.

This should help, we'll add it to the documentation as well. 
Please don't hesitate to comment if that's not working for you.