AutoCAD LT :: Disable Save As DWG When Saving DXF?

I have a software program that imports DXF files and converts them to its native format, so they can be used for simulations.  I use ACad LT to convert DWG files to DXF for this purpose.  Sometimes they don't import properly, so I may have to re-open and tweak the DXF several times to get it to import properly.  (What can I say - the target application is published by the government; of course it has issues.)  The point is that I often have to work extensively in the DXF format.

Every time I try to Save my changes, ACLT tries to save my DXF as a DWG.  It pops up a Save As dialog (which I did not ask for) and defaults to a DWG - I have to go back down the list and re-find my DXF format.  Every time.  Every. Time.  Then when I close the file (even if no changes were made since the last save) it pops up another dialog to ask me if I'm sure I wouldn't rather save the file as a DWG before exiting.