Yes. Last time it happened by me, I had 1-day games and 3-day ames (and I still have). Vacation was triggered for a 1 day game which went down to 90 minutes, and when I came back I had 24 hours. However, with the 3-day games they moved down from around 2 days 16 hours to 1 day 16 hours (40 hours)...
is my opponent cheating the clock?

So the time was added to your one day games, and it was substracted from your 3 day games? I very much hope that this is just a bug, and that it will be possible to fix that bug quickly!

TheGrobe, let us look at this scenario:
A premium member is playing an 1 move/day game, and he fails to make it before he loses on time. Auto-vacation kicks in a few minutes before timeout - he is put on vacation automatically. He comes back, and removes his vacation status.
Now, if automatically one day's worth of time is NOT added to his game, he times out (or again automatically goes on vacation) before he can even go to the game(s) page(s)! So one day's worth of time is taken from his vacation time, and added to all the games that were paused.
Please note that there is a recent change that each time a person goes on vacation (even for a second), at least 1 days worth of vacation time his removed from his balance (this is to prevent vacation abuse).
Does that make sense?
It would make sense if the person on vacation is about to time out on his games. But if he has 11 hours remaining for his next move, why should he be allowed to add 1 day of vacation time to his clock? They are defeating the purpose of vacation time. The idea is to have some breathing room if you are about to time out, not to have an extra day of time whenever you feel like it.

Eo, for me, vacation time can be a day (or some days) off chess when I need it, and I think many people would be perfectly right to feel the same way, wouldn't you think so, too?
The nice thing about correspondence chess is that it allows people to play chess when they have the time for it, within some agreed time framework that includes not only the time per move, but also the vacation time.

I would not view this as something personal, it is just about how the vacation system is set to be working in general.
For you, it does not make any difference at all whether he takes a day off on vacation, or if he takes part of a day of vacation and possibly has his clock ticking a little longer for that move. So I'd say you need not worry about this at all :-)
Why can't we see how much vacation time players have left unless they're actually on vacation?
I can understand that part very well when I see how unnecessarily preoccupied many people are being already now about other people's use of vacation.