Hi Jeroen,
If you remove the property "optimize=true" on the maven-compiler-plugin, your issue will be fixed. Indeed, with this option, line numbers are removed from the bytecode and Cobertura has no way to "link" bytecode to source code.
It's why you get the those kind of warnings in your log file :
[cobertura] WARN [main] net.sourceforge.cobertura.instrument.ClassInstrumenter - No line number information found for class nl.belastingdienst.wdp.beradmin.provider.BerichtDTOValidator. Perhaps you need to compile with debug=true?
Regards,
Freddy