Log-rotation FeeBSD 8.2

[newuse at qip.ru]

Hi all, something strange:
I am trying to setup newsyslog to rotate logs of FreeRADIUS 2.1.11
my setup string is looking like
[code]
/var/log/radius.log freeradius:freeradius 644 7 5 * Z
[/code]
but after rotation no logs are writing to /var/log/radius.log until restarting freeradius

But if I just run
echo "" > /var/log/radius.log
all logs are clean and writing well

What am I doing wrong? 

--
Best regards,
NewUse.