The reason:-

http://support.microsoft.com/default.aspx?scid=kb;EN-US;838910
Controls move to the left of the worksheet in Microsoft Excel 2002

But Jim Rech recently posted this:

This article is now obsolete. Since the 10/12/2004 security patch
there is no need to get a hotfix (although this article does not directly
mention this fix, it's in there).

http://support.microsoft.com/default.aspx?scid=kb;en-us;832332

But Myrna Larson posted that it didn't work for her in all her workbooks.

To apply the workaround to a number of controls, Dave Peterson recently
posted this:-

Maybe you could use a macro to fix the controls on the sheet.

If you want to change every OLEObject, you could do this:

Option Explicit
Sub testme01()

   Dim OLEObj As OLEObject
   Dim wks As Worksheet

   For Each wks In ActiveWorkbook.Worksheets
       For Each OLEObj In wks.OLEObjects
           OLEObj.Placement = xlMoveAndSize
       Next OLEObj
   Next wks

End Sub

If you want to be more conservative and only fiddle with the checkboxes:

Sub testme02()

   Dim OLEObj As OLEObject
   Dim wks As Worksheet

   For Each wks In ActiveWorkbook.Worksheets
       For Each OLEObj In wks.OLEObjects
           If TypeOf OLEObj.Object Is MSForms.CheckBox Then
               OLEObj.Placement = xlMoveAndSize
           End If
       Next OLEObj
   Next wks

End Sub