When I set inheritPixmap to true in ~/.Xdefaults urxvt
has a small (1 or 2 pixel) border around it that has
colors from the applications behind it (see screenshot
at bottom). I am using version 3.1 of urvxt.
Tested with blackbox and xfce4.
Please let me know if you need more info.
picture here:
http://www.prism.gatech.edu/~gtg722b/showme/urxvt-borderbug.png
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user_id=754477
Maybe it's not a bug, but a feature.
Adding the following line to my ~/.Xdefaults seemed to fix
the problem:
urxvt*internalBorder: 0