See similar issue at http://jira.codehaus.org/browse/IZPACK-610
The problem is that solution for this problem was not ported to simple finish panel.
Would you have a chance to prepare a patch?
Nope, but the solution is the very same from IZPACK-610
String path = translatePath("$INSTALL_PATH") + File.separator + "Uninstaller";
String path = translatePath(idata.info.getUninstallerPath());
in the SimpleFinishPanel
The fix is in, thanks!