[racket] 2 keystroke keybindings disappear

Is this expected behaviour?

I'm using the customization example in the documents

When I add this line instead of the last line 

;(menu-bind "c:a" "Run")
(menu-bind "c:x;k" "Close")

all the existing control-x bindings go away.  

So once I do "Edit->Keybindings->Add user-defined ..." 

C-x:C-s ignores the control x and starts the search function
C-x:C-f doesn't open a new file, moves the cursor ahead 
C-x:u   inserts doesn't undo, inserts "u"