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With a special combination of shell (zsh w/ syntax hightlighting), terminal (urxvt) and configuration with Xresources, I noticed a strange issue with font rendering that only seems to occur with some bold characters (AKA bold escape sequences) like the letter 'k' -- it will show up as a tall, empty vertical rectangle (see picture below):

terminal shows strange font rendering

Why does this happen?

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Post your configuration! (Especially the fonts but do post all applicable resources.) – Gilles Apr 24 '14 at 23:12
@Gilles I actually know the answer to this, but didn't realize that I had to wait to self-answer since I didn't have an account for this exchange :) (I'm only minimally active on SO) Spoiler: The culprit is the letterSpace resource being set to -1 in Xresources. – Isaac Aggrey Apr 25 '14 at 0:45
up vote 2 down vote accepted

The issue is due to the letterSpace configuration in the .Xresources file, which sets letterSpace to -1 (or lower) like:

! /home/username/.Xresources

URxvt*letterSpace: -1

Many users and blog posts will suggest changing the letterSpace option to -1 to adjust for kerning, but there seems to be a side effect in this situation where urxvt can't render the glyph.

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