Hello,
forwarding from http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=524776.

GtkMenuItems have too much padding at their ends since the upgrade to GTK 2.16.
I didn't find a setting for this in the GTK Reference Manual, so I filed this bug.
Downgrading to 2.14 shows the previous look, so I made screenshots:
Before: http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=GtkMenuItem+Before.png;att=1;bug=524776
After: http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=5;filename=GtkMenuItem+After.png;att=2;bug=524776

I don't know whether this is a bug or not, for sure it's an undocumented feature/change between versions (or at least I haven't found anything directly related in NEWS). Something related from 2.14.x to 2.15.x:
- The GtkMenu::arrow-placement style property allow more space efficient
   layout of scrolling menus
- Submenu arrows can be scaled relative to the font size, with the
  GtkMenuItem::arrow-scaling style property
538782 Make GtkMenu's arrow size themable
322934 Replace menu's proxy icons with empty space hiding icons