This is the icon. It is PNG 48x48 with alpha transparency

Right side of following pictures is important.
1.2.14pre1 on left pre-rendered XPM 16x16, on righ resized PNG 48x48 -> 16x16


1.2.14pre10 on left pre-rendered XPM 16x16, on righ resized PNG 48x48 -> 16x16


1.2.14pre11 on left pre-rendered XPM 16x16, on righ resized PNG 48x48 -> 16x16


1.2.14pre - top with Xft, lower only corefonts - when AA (Xft) enabled then fonts are not placed in the middle of buttons, but are shifted bit down.

You can also note a different size of text (1.2.14pre1 had bigger fonts with same settings).

config.log for 1.2.14pre11, others compiled with same options

preferences::

TaskBarShowWindowListMenu=0
TaskBarShowShowDesktopButton=0
IconPath="/home/test/.icewm/icons/menuitems/"
MenuIconSize=16
SmallIconSize=16
BTW: This is how IceWM draws PNG 48x48 with transparency when MenuIconSize=48. Left pre-renderd XPM 48x48 with grey background, righ PNG 48x48. Note borders are not shaded. Probably all pixels with transparency are cut out.