Changes in Winbox not properly applied

Following issue:

I have a CCR1009 patched to latest 6.19.
I have created a L2TP/IPSEC-szenario with radius. Works fine.

I changed in Winbox the setting /ip ipsec peer nat-traversal=yes

lateron I changed it back to nat-traversal=no

This change was not applied, the NAT-traversal was still in effect. In Winbox the checkbox was clearly unmarked.
After a reboot of the CCR the NAT-traversal was disabled properly.

Is this a bug? Am I doing something wrong? Must I “apply” a configuration change? SHould the L2TP-Server be restarted after a change to apply it?