Visual Studio corrupts its settings with regular monotony (always has done, I've been suffering from this since the Visual C++ days, and it's still a bugbear in VS2013).
Often this seems to be totally at random, but it's highly probable after a crash.
It will also lose any changes to your settings if Visual Studio doesn't shut down cleanly - for some reason instead of saving back the settings when you OK the dialog, VS seems to wait until it quits to write back your changes, so after changing options I always quit and restart to ensure the changes have been flushed to disk. Similarly you should never change options with 2 or more instances of VS running, as the last one to quit will overwrite the settings.
In particular, there is an easily reproducible case: If you launch two or more copies at the same time (by which I mean if you start up two or more copies, so they are all initialising at the same time), they seem to fight over the settings file and it becomes corrupted or resets to defaults.
The best two workarounds I've found are:
Never launch more than one instance at a time. If you need to run several instances concurrently, then wait for the first one to finish loading its Solution before you start to launch the next.
Always use Tools > Import and Export Settings
to save your settings to a backup file, so that recovering from this corruption only takes a few seconds each time it happens.
Another smaller, but still rather irritating habit is that if VS is minimised when it is quit (e.g. by shutting down), it corrupts its window position information and the next time you run it, it will be maximised.