To prefix this issue I am to not able to reproduce as of yet.
Last night 2015-05-27 approximately 23:30 GMT +2 (Stockholm Time) the Realms server that me and a bunch of friends play on got the regular and expected "Minecraft Realms is going to restart" message. Most of us hang around for the server itself to kick us and as soon as it came back up we promptly logged back inside. To our contempt we where no longer where we had logged off. The Realms server had reverted to a back up save from approximately 30 minutes back in time before the restart. This feels unacceptable and I know not where to turn but the Bug Tracker. A lot of progress was reverted by that restart. May it never happen again.
Is this still an issue in the current Minecraft 1.8.8 or later? If so, please update the affected versions in order to best aid Mojang ensuring bugs are still valid in the latest releases/pre-releases.