Crash dumps not working correctly for amd64?

[Sean Chittenden]

Howdy.  I've got myself an interesting situation.  It seems as though
amd64 is unable to collect crash dumps via savecore(8).  Has anyone
else seen this?  From dmesg(1):

Checking for core dump on /dev/da0s1b ...
savecore: first and last dump headers disagree on /dev/da0s1b
Feb 21 12:45:59 host savecore: first and last dump headers disagree on /dev/da0s1b
savecore: unsaved dumps found but not saved

???  sys/amd64/amd64/dump_machdep.c and sys/i386/i386/dump_machdep.c
are essentially identical.  I'm not familiar enough with these
innards, but reviewing savecore(8) didn't point out anything obvious.
I'm dumping onto a twa(4) controller.

Are there any known workarounds to get this info?  I'm tempted to turn
off swap in fstab(5) that way the next time the machine comes up after
a crash, it'll still have the dump in tact and could poke at it as
time permitted.  Other suggestions?  -sc

-- 
Sean Chittenden