Issue with DocumentBeforeSave Event

We have a Letters application(VB6) which opens the word document and the user
does some changes in it and save the file. We wanted to prevent the user from
saving the document with different name and we have added the following piece
of code in the documentbeforesave event

If Ucase(strFileName) = Ucase(Doc.Name) then
SaveAsUI = False
End If

This served my purpose and it is not displaying the Save As dialog box when
the user click on 'Save As' from the file menu.

The problem here is
The VB6 application opens the word document and by default saves the word
document with the name 'Letter_Template.doc' and the user modified some
contents in it and left it idle for 10 min and did some change after 10 min.
After that when they tried to close the word document, the word prompted the
message 'Do you want to save the changes to ~WRLxxxx.tmp' file.

Why the word document changes the filename from 'Letter_Template.doc' to
'~WRLxxxx.tmp'.

And when trying to find out the reason, I tried it by turning off the 'Save
AutoRecovery info every 10 min' then the application was working without any
problem.

Why it is working fine when I turn off the AutoRecovery and why it is not
working with AutoRecovery on?

Am I doing anything wrong here or it is the defect?