@Anonymous
I would have to take a look at your render settings to see what you have selected. Are you running any renders via a command line? or do you have any instructions in your render options? Again I would either need your file to see your settings (you can empty the models and asset and PM me a link if you want, yet I would need to see how this is being rendered) Also if you can provide me with a render log so i can see what is going on.
What version of Maya are your running? What render engine are you using? without these, it is very hard to give you a concrete answer, as you must have a command running that is Making Maya render 2 types of files. You also might have several layers with different overrides that are rendering as different image formats.. this is all in your settings. Please take a look a this documentation: Maya Render Settings
Let me know if this helps
