Under Windows XP Pro x86 SP3, changing the toolbar icon size from Automatic to Large (Tools, Options, LibreOffice, View, Icon size) has no immediate effect on the main toolbars (only after restarting LibreOffice). This is a regression from version 3.3.x where icon size changes were applied immediately to all toolbars. Curiously in versions 3.4.x and 3.5.x it applies immediately to the Formula Bar in Calc so this may be a clue to what should be changing.
*** This bug has been marked as a duplicate of bug 35972 ***