I am using a m425dn and I have the same issue. I updated the firmware to 05212014 and now we cannot print any font size larger than 48pt. It doesn't matter what program or font you use. Although I was able using Powerpoint, not sure if it resized the font.
If a page contains 2 different font sizes, (i.e. 48pt and 72pt) the Smaller font will print, but the larger font will not.
I have:
1. reset the printer settings.
2. Tried a different computer, that didn't have the printer installed on it.
I am going to contact support to see if there is an issue.