Yes some of them only exists as 16x16.. Will have to see If I can find some replacement for them..
Think it is the Refresh, Back, Forward and History button.
And the icons would also look a lot better in Medium size (24x24) if the icons supported that size. right now only 16 and 32 are support in most of the icons. So when choosing 24 or 48 icon size the icons are scaled. And the on XP the Medium size look worse then on Vista/Win7 since XP will scale up the 16 icon to 24, on Vista/Win7 the 32 sizes icon will be scaled down to 24, that looks better.
Best would be the have icons that are 24 from the beginning and not scale at all. But that is not an option at the moment since I can not draw icons my self. (Well I can. but they will look very very ugly)