kokoko3k, I want to thank you for your post. I noticed the same problem but had no idea it was fixable via removing the namil font. Some searches sent me here. I posted the bug here
https://www.rockbox.org/tracker/task/13090 .
I was wanting to download an alternative set of fonts, or to remove the fonts that cause the issue. So, I went to
http://dl.dropbox.com/u/30204410/Rockbox%20as%20an%20Application/Font%20Pack/font-pack.zip , which is a listed url for an alternative set of fonts on the rockbox extras page clickable on all pages under the rockbox.org domain. However, this url did not work for me.
I also emailed Hayden Pearce since it is his link. That was several days ago. No response.
I can confirm that this font causes this problem, but the question is why. My wild guess is that if one did a test they would find that the bad fonts are outside of the spec or something. This might cause perhaps an overflow into memory.
Here is a workaround: whenever you download the fontpack at
http://download.rockbox.org/release/3.13/rockbox-fonts-3.13.zip , copy over the 08-Namil.fnt file with 10-Fixed.fnt file. (They seem about the same size, which itself supports the above theory.)
You might think that not using the font solves the problem but keep in mind that you can install dozens of themes and some use the bad font(s) in all sorts of ways.
A developer should probably replace the offending fonts in the zip file on the server, but I think we need to confirm which fonts cause the issue. Perhaps someone else will chime in with their own reports? Fonts don’t matter much to blind people, who are the best audience to complain about the voice features, so it is a slightly tougher bug to fix than normal, arguably.