Mrs CO FF's sticker balance shows the following:

PREVIOUS BALANCE 3
04/28/07 AA *** LAX BOS -4 -6 -6
04/27/07 PURCHASED 3 3
CURRENT BALANCE -1 0 0 0 -6 0

(she had 3; on 4/27 bought 3 more; on 4/28 flew LAX-BOS and used 6).

What's confusing is the "-4" under "Purchased" next to her flight reference. Note that it doesn't show up in the "total" column, nor does it impact the "Current Balance" total (which is correctly zero, unless I think she'll clear and I buy her more...

Any idea what happened here?