The current Ant release is 1.7.0. You use release 1.6.5; it has a bug that has been fixed.
All right, if you really want to know, the bug symptom is that org.xml.sax.SAXParseException.systemID is incorrectly encoded. The Ant folks thought the transcription of an URL via UTF-8 to %XX-encoding takes a string and returns a string; this assumption is very incorrect.
It should take a string and it should return a byte array (because Java does not support multibyte characters as such, and in parallel to what java.io.PrintStream ultimately does). I do not know whether they have fixed it or devised a workaround to make the code even more illogical and erratic; whatever they have done, the problem is gone in release 1.7.0. That is all for now.
My suggestion is to switch to the current Ant release for driving the build process ASAP.