If all of a sudden you notice that the SELECT elements in your Drupal forms increases to 4 and any smaller size is ignored...

... maybe you've already forgotten you were using Chrome, and it is not a Drupal bug : this is a "usability" feature of WebKit. See http://trac.webkit.org/browser/trunk/WebCore/rendering/RenderListBox.cpp#L67.

Safari users are probably used to it, but for users of other browsers, this is a bit disconcerting.