^Z during port build and hang?

[YONETANI Tomokazu <qhwt+dfly@xxxxxxxxxx>]

Hello.
Recently I'm gettings hangs(on today's HEAD) if I press ^Z while
building a port.  It seems that I can correctly suspend the
processes for a few times, but after that, it just displayed
^Z and started ignoring ^Z or ^C(it responded to ^T and displayed
the hanging process and its state), and the load average slowly
grew up. I tried to switch to other virtual consoles or ssh from
another machine, but it was too late, I couldn't even log in.
I have no problem unless I tried to suspend the make process,
so this is basically
"Doc, it hurts if I do that -- don't do it, then"
problem :). Is anybody else seeing the similar thing?