Have yet to take cmvsm seriously. This is in line with what an Apple Manager told me.. he didn't mention this exact "F" situation but an Inventory Manager explained to me how the issue would be found/identified and resolved but it might take a month or more.
I have been entertained how certain posters here have kept telling us we should accept this all the while most who have spoken to Apple have been told it is NOT how the iPad should be and is, and I quote the Apple Store Manager,"A warrantable issue".
Lol...the letter 'F' simply means that the iPad was manufactured in the first half of the year. Good luck with your magic fix. Maybe Apple will share the pixie dust with Sony, Samsung, and LG. At least the Apple Manager got you out of the store to extend his lunch hour by 15 minutes, hoping that within the month timeline, you will have either forgotten about it or just stop bothering.