gnucash records badly messed up

[Ross Boylan]

I've just discovered that my data in gnucash are in bad shape.  I'll
describe the symptoms, some things I did that probably contributed to
the problem, and then ask for advice on recovering.

Here's a SUMMARY for the impatient:  At least one transaction has
vanished, along with a few other peculiarities.  I was running gnucash
on 2 systems and syncing the files, but I did so imperfectly.  I also
just upgraded from 2.2.3 to 2.24.  I have backups.  How can I recover,
without losing my recent work?

PROBLEMS
The major problem is that my balances are way off, even in accounts I
reconciled.  A transaction seems to have disappeared.

I have an account which corresponds to a bank account, and it shows a
huge negative balance.  This account, among other things, receives the
cash proceeds of stock sales.

The stock account always had problems because of gnucash's insistence on
rewriting certain splits (see
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=443608).  However, they
seemed to have ended up OK. Now one of the splits (the one with the
stock account and the capital gain offset) has jumped into the shares
column, so that the sale now results in a huge increase in holdings.
I've tried to edit it back into shape, but the program keeps changing
around what I enter.

Something like the dollar proceeds do show up in the account that got
the proceeds.  However, a later stock sale has vanished entirely from
both the stock and bank account, resulting in the negative balances for
the latter.

A minor problem preceded the major one.  A week or two ago when I went
to reconcile an account I was unable to post a divident to the account
through the usual window that pops up at the start of reconciling.  It
would not let me select an account for the funds.  Since that window has
always been a little peculiar (the accounts I needed to select didn't
seem to go with the labels on the subwindows), and since I could enter
the dividend manually and was pressed for time, I ignored it.

POSSIBLE CAUSES
I was using gnucash on 2 systems, using unison to keep them in sync.
However, some files weren't writable, so I skipped them.  I may also
have prevented it from deleting some files or syncing them over (there
were some very old ones).

I also recently upgraded to gnucash 2.2.4.from 2.2.3.  The upgrade
preceded the major problem but followed the minor problem.

I'm running on Debian GNU/Linux testing aka etch.

HELP
I would appreciate any help in restoring things to sanity, or in
understanding what is going on.  In particular, I don't really
understand what role the xac, log, LCK and LNK files play.  I have
backups, but I'm not sure what files I should restore and which to
delete.

I have work that I did after the last point I know things were good, so
simply turning back the clock is not a full solution.  Also, my strategy
while I was traveling was to backup on my home computer after mirroring
to it (in the funky way described above) from the laptop on which I was
working.

Ross