According to history, it's basically a save, as once the file is saved using save as, it's a new file, but it still has all the old history, which you can return to. You can't go back in history to the original file. Once you do a save as, the original file remains in the last saved state prior to the save as.
I'm not seeing what you're seeing, Jeff. I just get a save. I tried what you did with a new doc, and also older docs, using save as to keep the same file type and to change the file type. All showed just save.
I open a tif file , save as psd , duplicate a layer , save as jpg .... the panel shown "Save" , not Save As .... IT SHOULD BE SHOWN SAVE AS .
Next step, I quit it, PS prompt me if need to save before quit. That means I didn't save this file , but the history panel show "Save"... If I want to see the history panel to recongize what I done before, that will be in trouble. The history told me I "SAVED"
In previous version, it doesn't like that. I use "Shift Control + S", Save As, the history panel will shown "Save As"