* the OnMessage routine (starting at line 442) does not handle the message types GUI_MSG_SELECTED and GUI_MSG_DESELECTED, the base OnMessage routine will be called only
* the variable "checkMark" must be set to the same value as "Base.Selected", otherwise the checkmark doesn't change the state
* this is an enhancements to support special API calls
* source code file: mediaportal\core\guilib\GUICheckButton.cs

h4. Steps to Reproduce
* add a skin control element "GUICheckButton" to source code
* call the API function "GUIControl.SelectControl()" or "GUIControl.DeSelectControl()" with the appropriate values
* expected result: the checkmark changed
* current result: the checkmark doesn't change, it's only possible to set the element value "Selected" to true/false
* for more information, please take a look here (http://forum.team-mediaportal.com/threads/question-regarding-guicheckbutton-suggestion-to-fix-fullscreen-related-problems.114872/#post-947418)


h4. Additional Information
* a test plugin can be found here (http://forum.team-mediaportal.com/threads/question-regarding-guicheckbutton-suggestion-to-fix-fullscreen-related-problems.114872/page-2#post-950761)