Jeroen,
Crdit for the solutions goes to Ceri Davies who pointed out that there
is a line in /etc/rc.subr reading:
$_procname|$_procnamebn|${_procnamebn}:|"(${_procnamebn})")'
Which must be changed to (one line):
$_procname|$_procnamebn|
${_procnamebn}:|"(${_procnamebn})"|"[${_procnamebn}]")'
This worked for me on 6.0 Release.