I have a similar problem, but with the text appearing condensed horizontally, like in the opening of the The Matrix, in all the detail symbols in a file. However, when I edit the symbol and one of the misbehaving callouts, adjust its font size, for example, all the callouts correct themselves, not only in the particular symbol, but in all symbols in the file. Then when I reopen the file it's fixed. However, it's doesn't always stay fixed.