My guess is that something is broken in the softdep changes, but I
don't know for certain.

I also noticed a serious difference between 1.4M and 1.4O -- my system
now locks up with the hard drive light on when I get a missed
interrupt message.

Before 1.4M (probably back to 1.4G or so) my machine never had a hard
drive problem unless it spun down.  With 1.4M, especially when using
the IEEE WaveLan driver, the hard drive reports missed interrupts (and
the USB controller reports it received an error and was shutting down)
but still recovered by falling back to PIO mode.

With 1.4O, I get the missed interrupt message from pciide0, and then
the system locks up tight.

--Michael