twitter/bootstrap — pull request #4184 by alejandrogarciaiglesias (2012-07-25 16:28:43+00:00)
Title: Prevent buttons from breaking on hover when using custom colors

If you only change the @btnBackground and @btnBackgroundHighlight variables for customizing default button colors you always have a semi-white background when you hover the buttons. This way, the background hover animation still works and prevents it from breaking your custom colors.