Hi dragan
I also experienced the same problem and I also solve it using the keyboard macro. Ive notice that the cursor will not be updated until you lost focus

  ** Checkbox:Init
  ** This property allow to track for change
  ** You can also define it early if you have check box class 
  this.AddProperty("needChange",.f.) 		

   **Checkbox:InteractiveChange
  ** This line check if in edit mode its depends on how to trap it

   If Thisform.sjdbhandler.editmode  Or Thisform.sjdbhandler.addmode

     ** Flag if there is a change in check box.
     ** This property is created at init event

 	this.needChange=.t.

     ** Envoke LostFOcus by just simulating of pressing TAB  after clicking the checkbox
     ** I this case this will trigger the lostfocus
   
	KEYBOARD '{TAB}'
    ENDIF

     *** Checkbox:LostFocus 
 
         ** At the lost focus , check if the value change then reset the flag 
         ** and do the computation    
	 If 	This.needChange=.T.
		This.needChange=.F.
	
	       *** DO YOUR CALCULATION HERE
         
	Endif

HOpe this help.