In XP in | control pannel | display | Appearances tab | Advanced | a person could select and ODD size for ICON, and then icons would be resized , this could effect the systray icons and standard explorer icons. the "default" is 32, but an odd setting like say 37 could cause weird interpolations like that.
Also other odd size settings , in there have effected other things, like the height of the Title bars, and text sizes.
Other things might be some utility or something that is adjusting the size of those with some other zooming routine? Of course a Theme could set that item, and a theme could retract it again , just when you thought it was fixed.
I do not think that setting an ODD DPI would effect that, but mabey? DPI would be in | Control pannel | Display | Settings Tab | Advanced | General Tab |
Because it is shown well on 2 icons , it could just be that the icons chosen for display are some sort of 16pix or 24pix icons instead of standard 32pixel icons.