If that doesn't set off just about every warning bell in your head, consider that Ant performs character set decoding and re-encoding when copying files. By default it will decode every file with your system's default character encoding and then re-encode it with the very same format. As far as I can tell all this can possibly do is introduce errors. When copying a binary file the best-case scenario is that your JVM throws a runtime error, but it's more likely that ant will silently corrupt the copy.
The Ant team's solution for this problem? You might reasonably expect that they would provide an option for binary files which does a byte by byte copy. Instead they suggest that you change an environment variable to an encoding which "does not seem to contain illegal character sequences."