Strange Symptom of Running Out of Disk Space
Recently we had an issue with SharePoint Search that caused very large log files to be produced, eventually taking up almost all the hard drive space. Restarting the server (without yet knowing this was the issue) produced a problem wherein a custom top navigation tab on the MySite pages was duplicated, appearing twice side by side between the MyHome and MyProfile tabs. This navigation tab was created from Central Admin (Shared Services Administration> SharedServicesName> Personalization site links), and was not custom developed.
Since both duplicate tabs were fully functional (if quite distracting) I left them for the time being to find the cause of the trouble. Once the log files were moved and the drive space restored, a restart outside of production hours corrected the problem.