The application I\'ve been developing uses ActionBarSherlock, and the main theme inherits from Theme.Sherlock.Light.DarkActionBar. The design requires that the overflow menu pop
I think that due to the fact that Theme.Sherlock.Light.DarkActionBar don't style its contents right is due to the actionWidgetTheme attribute is used with a ContextThemeWrapper for inflating the action bar views (Jake Wharton's own words), thus something like the following (not tested) will be needed to fulfill your needs, though breaking your need of not using Theme.Sherlock as parent in one way:
Might work or not work. That's the question :)