This is covered by bug 1603688 (https://sourceforge.net/tracker/?func=detail&atid=105470&aid=1603688&group_id=5470) I implemented 2 versions of this patch. One version raises ValueError when an invalid interpolation syntax is encountered (such as foo%, foo%bar, and %foo, but not %%foo and %(dir)foo). The other version simply replaces appropriate %s with %%s. Initially, I believed ValueError was the appropriate way to go with this. However, when I thought about how I use ConfigParser, I realized that it would be far nicer if it simply worked. I'm +0.5 to ValueError, and +1 to munging the values.
For the record, this was supposed to be a patch. I don't know if the admins have any way of moving it to that category. I guess that explained the funky categories and groups. Sorry for the inconvenience.
