I'm almost "extremely confident" about this being a software issue, so here it goes
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I've used this font this morning: http://openfontlibrary.org/en/font/ruji ... font-v-2-0
I had no trouble at all using it, but when I opened my drawing again, the red exclamation mark appeared and Inkscape tells me it can't find the font on the system. I'm sure I haven't changed anything on my system or the place where I store the font (/usr/share/fonts/truetype). I've noticed it happens also with other fonts that were on Ubuntu, such as "Sans".
If I select the text and open the font list, the font's name appears as striked text on the part of the recently used fonts and I can't select it. But if I go down and select it from it's place on the whole fonts menu, I can.
Maybe I'm missing something... Any ideas?