In particular case (confirmed by ESRI tech support) a user was using copy/paste from a cell in an Excel worksheet to the version name field in the version properties dialog box when creating a new transactional version in our enterprise geodatabase. When user copies the cell from Excel, a carriage return is at the end of the text string value that Excel places on the Windows clipboard. When this is pasted into the version name field of the version properties dialog box, the carriage return goes in with it - as a nonprinting character - which is extremely easy to not notice. Turns out, later on, that version names with non-printing characters in them cause problems when switching to that version at a later time.
This idea certainly suggests that - in general practice - for user input into text fields in dialog boxes the software should either filter out non-printing characters, or at least warn the user that they've entered non-printing characters. Since pasting values from the clipboard that came from other applications is a common practice in Windows - the software needs to perform some sort of validation on these pasted values so that problematic characters don't get entered and accepted as input.