Fonts are transmitted in the assets.dat file. Make sure that you rename the assets.dat file prior to uploading to our server. The product files are stored in one directory and if you don't rename this file, then the assets.dat file that the program will use will be the very latest assets.dat file. It might not be the assets.dat file that you uploaded for a particular product. So, the point is, rename this file to a unique name (keep the .dat extension) and you will have the right fonts for that product.
If you want a specific font for a product you need to follow the below instructions.