This seems to me the same behaviour for both. The problem is not really the black boxes, they usually simply mean a missing glyph in the font, but the problem is that somewhat in the text is triggered the use of two different fonts.
Unfortunately there's not much we can do for the SQL error. I think the forum software has some problems with Unicode text. A workaround to submit a sample of text is to use the attachment function with a ZIP file, or possibly one of those online text sharing services.
Edit: I read a bit about the SQL error and it seems not a phpBB bug but it's possibly about the MySQL DB, they point to this article
http://www.phpbb.com/kb/article/doesnt-have-a-default-value-errors/. But I think it's low priority and something to look at when the time permits and with a full backup of the board. I don't know if/when Alex can look at this
