This might be because I have been using the "bleeding edge" Raspberry Pi build ... but the documentation at openelec.tv/installation/updating says:
"From the folder you extracted the new release into, open the target folder. Inside you should find four files. Grab KERNEL and SYSTEM from here (ignore the MD5 files) and copy them to the update share on the OpenELEC machine."
I tried it today - and did not copy the MD5 files over ... and the update process reports a problem with the files missing and does not perform the update.
I then copied in the .MD5 files and the update went fine.