Unlocked cells in pre Excel2013 versions become Locked in Excel 2013 problem

[Newton51]

I have a workbook which i use for technical analysis. It works perfectly in Excel 2003, 2007 and 2010. However when i use it in 2013 if I try and type in an unprotected cell Excel treats it as protected, even though Properties clearly show Unprotected. This happens only after I have used another "navigation" type macro (to say, a sheet containing a full screen graph of the data set). When I return to the data input sheet, all unprotected cells are now locked. I can modify some of the numerical data by using a pre-existing slider control but I cannot modify text because of this "Excel 2013 locked cell phenomenon".

All sheets are Protected and any cells used for editing are set to be "Unlocked".

This is the macro to navigate from the Create sheet (when correct cells are unlocked) to the Graph:

Sub myNavGraph()
' Navigation macro to Graph
    Sheets("Graphs").Select
    Range("A1").Select
End Sub
[\CODE]

This is the macro to navigate from the Graph to the Create sheet and then the former unlocked cells are now locked:
[CODE]
Sub myNavCreateMix()
' Navigation macro to Create screen
    Sheets("Create").Select
    Range("e2").Select
End Sub
[\CODE]

All of the VBA works perfectly in pre-2013 Excel versions so I am  stumped about why this is happening since installing Excel 2013.
 

  I have been seeking some confirmation this is happening to others via  Google search and found one (only) similar reported event.  There was a  response suggesting "the bug is in opening files from a modal UserForm  and the solution is to open a UserForm as modeless. A link to microsoft  was explaining about "SDI"  

  
It would be great if some kind person can let me know how to modify for  compatability with Excel 2013 so the selected Unlocked cells are  permanently Unlocked.

   TIA