The problem with sd cards is what they call delayed writes.
The write operation seems to have finished, but the os still needs to write some stuff to the card in background.
Removing the card 2 early can also corrupt the card file system. This can also be a reason of malfunctioning.
If your computer is having an internal cardreader, it's hard to know when a copy operation to the card really finished.
It's a serious design fault.