I have had VirtualBox 4.3.6 "forget" my runtime state a few times over the last few weeks / months (if you include other versions).
I'm running Linux Mint guest on a window7 host. Every few weeks, when I lock my windows box (ctrl-alt-delete) when I return and unlock the Virtual machine as disappeared. Sometimes when restarting I have lost all my runtime state. Today I lost a week. Luckily everything was checked in to source control. In fact that's how I noticed, all my recent checkins vanished from my local copy and I had to resync to get them.
I have the remember runtime state box checked.
Makes me feel unsafe about working in this VM unless I shutdown everyday.
Anyone else experienced this?