I have a 1TB microSD card in my Sansa e280v2, formatted to FAT32. A minor issue that has always bothered me more than it should is that I cannot reliably transfer files to it from a computer via the cable to the Sansa - some files get copied, then it hangs and fails. Sometimes the whole card filesystem gets corrupted in the process and needs formatting. It is not a big deal in practice, as I take the card out and use a dedicated SD adapter to write instead, that works flawlessly and is probably faster anyway. Once the card is back in the Sansa, it has no issues browsing and playing the tens of thousands of files.
I always blamed this on the outrageous card size (by 2006-standards), or maybe my Sansa was a bit broken, I thought. However, now more by accident I noticed that I can transfer loads of data to the card in the Sansa via the cable if I boot it into the original firmware first. Is this expected behavior? Is there a way I can get the same transfer reliability when it is running Rockbox?