I see a lot of users who have the Save Settings on Exit option toggled on in their User Preference settings. While this can be a great benefit to have the active graphical settings saved in your design file when you close it, the setting does carry some risk.
In my user preference settings, I keep this setting turned off, preferring them to do a manual Save Settings when necessary.
We all have those moments where we inadvertently click something and strange things start to happen. We have no idea what we may have clicked, much less how to undo what we just did. This happens quite a bit with new users during training. When this happens in MicroStation I close the file, exit MicroStation, and start again. Since I have the Save Settings on Exit option off, any stray graphical setting that may have been changed causing the odd behavior does not get saved in the drawing.