my program did not have this problem until today. when i choose to export in MP4 format the program only exports with a .3gp extension and format. i am using windows and magix edit pro version 16 download.
When I go to the 'Export movie' >> 'Video as MPEG-4...' window, the file extension depends on the preset I've chosen from the top drop down menu, or used as a base for a custom format. Only a very few are 3gp so why not pick something different? I've no idea how MEP could change things on its own.