processes freezing when writing to gstripe'd device

I'm running current from around the 24th of July. About to build world
to see if it makes any difference.

I am observing processes performing operations on a gstripe device
freeze in state 'bufwait'. An 'rm' process is stuck right now. The rest
of the system is fine.

The devices are two vnode backed md devices which I created just for
testing. The same thing occurred using two freebsd partitions of size
15G each (not slices).

       NAME: test_cd.stripe
  geom name: test_cd.stripe
  mediasize: 10231808 (9.8M)
 sectorsize: 512
       mode: r1w1e0
      state: UP
     status: total=2, online=2
  providers: md3 md2
       type: automatic
 stripesize: 4096
         id: 1411913070

What's the best way to look in to this? I can't attach to rm with gdb
(it just ends up waiting for something). I can drop to kdb, but have no
idea where to go from there.