Package org/apache/oro/text/regex sources come inside jython sources. Didn't check yet if they are altered from upstream in any way.
This is what ant manual says: Warning : jython.jar also contains classes from jakarta-oro. Remove these classes if you are also using jakarta-oro. The sources differed in implementation details from jakarta-oro-2.0.8, probably older version was bundled. It builds fine against jakarta-oro-2.0.8 and basically works. Fixed in CVS in jython-2.1-r11.