I have generated attached coburtura coverage.
There are several linebreaks eg. in line 39 which breaks the xml validation against http://cobertura.sourceforge.net/xml/coverage-04.dtd.

ut_coverage_cobertura_reporter.zip

Version:
OS: SLES 11.4
utPLSQL-cli 3.1.6.local
utPLSQL-java-api 3.1.6.411
Java-Version: 1.8.0_66
ORACLE_HOME: null
NLS_LANG: null