Confirmed. And each time you press the Apply button of any preference pack the more duplicates you get in the combo box. Affected are also the combo boxes for the list of style sheets and the view mode of the tree structure.
The issue is caused by the fact that DlgGeneralImp::loadSettings() is called each time the Apply button is pressed but the affected combo boxes are not cleared.
The second problem why the icon size is not applied is because the value of the parameter group isn't read from the parameters but the currently active value is used.
Both issues are fixed with git commit ff876bf72c