I've been running the Twitter Tools 1.5 betas for a couple of weeks on my site, publishing a daily digest around 23:30 local time.
Every once in a while I've noticed an extra copy or two of the digest showing up in the scheduled posts, scheduled for 24 hours later. I never got around to tracking down the problem, just deleted the extra posts.
Yesterday I upgraded to 1.5 final, and today I found something very strange: last night's digest had been posted on time, but more than 30 copies were scheduled to appear tonight! I cleared them all out, checked back an hour or two later, and saw another 3 copies had been scheduled.
I looked at the database, and aktt_next_daily_digest was still pointing to last night's time. I assume it just noticed there was a digest due, built it, scheduled it, but never updated the scheduled time.
I ended up hitting the button to reset TT, and the option pointed to tonight. So far one more copy has shown up, but it could have popped in between the time I cleared the old ones and the time I hit reset. I'll keep an eye on it, and post a followup if I see any more, either for last night's digest or for tonight's.
In case it matters, I'm in the -08:00 (PST) timezone, so at the time I've chosen, the local date and UTC date are different.