System reboot when assign GIF interface

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Hey guys, have anyone of you had such problem: I have set up GIF tunnel with Tunnelbroker (tunnelbroker.com). After the GIF is done I have to "assign" the interface, but the moment I try to enable the interface the OS reboots.
This is 100% reproducible. Never had real problems with Opnsense but this one is strange.
I'm using the last available version. There are no messages in the logs. It's just like I have pulled the power cord.
Even if I have mistake in my config, enabling interface should not kill the entire OS, right?!

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Hm, I've managed to assign and enable the interface via pretty random workaround - just changed the remote endpoint IP in the GIF tunnel.