User Scenario:

 Make it sure that an option "Automatic file name extension" in the 
 dialog "File Save As" is disabled before staring this scenario.

  1. Open a Word document file sample.doc with Writer.
  2. Choose the menu File - Save As. 
  3. Choose a file type "OpenDocument Text (.odt)."
  4. Press the Save button.
  5. Answer with Yes to the dialog asking if you want to overwrite it. 

 Now she gets a file sample.doc in OpenDocument file format. 

 It cannot be neither opened with Word on Windows because its content 
 is now OpenDocument nor correctly handled by a file browsing application 
 such as nautilus on Linux because an extension of the file is still 
 ".doc" instead of ".odt." 

 She recognizes she has lost her document. She might not think she did 
 anything wrong. She wanted to convert a Word document file to a OOo/SO/SS 
 document file following the directions that she had been instructed. 

 Additionally, there would be more complex situation. She can open the 
 problematic sample.doc on Unix variant because the system knows a file 
 of ".doc" can be loaded by soffice that can open it correctly despite 
 the wrong extension. Her contacts who received her document via e-mail 
 cannot open it with Word because they do not have OOo/SO/SS and reply 
 to her to send it again with a short message the file seems corrupted. 
 Without an experienced user's suggestion, they would never be happy to 
 achieve their tasks with OOo/SO/SS.

The story described above is a real story that I have heard.

Consideration from a perspective of User Experience might be needed to 
avoid users' bad experience that would diminish OOo/SO/SS.