Today I was trying to read a textfile from an SD card on the Hydra (with latest 4.2 firmware).
I was having trouble with the TextReader.ReadLine method, it threw IndexOutOfRange exception always at the same point in the file. After that I wrote my own ReadLine implementation with the FileStream.Read() method and suddenly a whole part at the beginning of the txt file became corrupt (it was overwritten with 0xFF’s).
Don’t know how that happened but I do know that I was only READING 
So there might be a potential problem that needs some attention.