Mystry in a Combo Box

A userform among other things has a combo box that .additem the contents of a select cell. It works fine until the user Freezes Panes and the button kicking off the user form is on the frozen bit of the screen and the selected cell is on the unfrozen bit. when the pane is frozen the .additem seems to pick up everything from where the the cell would be if the pane wasn't frozen down to where the select cell is. Similar things happen when the window is split. Why is this and how do I stop it.