I’ve noticed a really minor bug in LookAndFeel::drawTooltip(). If you make the TooltipWindow a child of a DocumentWindow in OS X instead of putting it on the desktop, there is no outline. Here is the offending code:
#if ! JUCE_MAC // The mac windows already have a non-optional 1 pix outline, so don't double it here..
g.setColour (findColour (TooltipWindow::outlineColourId));
g.drawRect (0, 0, width, height, 1);
Obviously the OS-generated 1 pel outline won’t apply to child windows.