A few weeks ago, I was looking on my Steam account, and it seemed like every game was showing up with an absurd about of hours played. 70 hours, 55 hours, etc.
Then I noticed, and it wasn't happening on games that I haven't launched, it also wasn't happening on non-steam game shortcuts. So, thinking back to what the playtime numbers used to be, I figured out that it was simply tacking on an extra 50 hours to whatever that number was.

Now, just today, I look, and I notice the "hours played being anywhere between 235-275, except for games that I've played recently, which are showing up with the correct time played. Also, whenever I launch a game, it will revert back to the correct number, so I guess It's not really a big deal. I'm mostly just curious if this is happening to anybody else, or has happened to somebody else in the past.

Yes, apparently Ive played 36 hours of the stanley parable demo.

I think it's affecting everyone, or at least everyone I've asked. I don't get ridiculous times like yours, but it'll add between 2 and 8 hours on, which is annoying 'cause now I'll not know 'til it's too late when I hit 400 hours in dota.

Yep, exact same thing's been happening to me, too. It's pretty annoying.

Every one of my games had 40 hours of added time. 41 hours for Dear Esther, 47 hours for Bastion, 65 hours for Faerie Solitaire...what, don't tell me you haven't played over a full day of Faerie Solitaire as well. Don't look at me!

I noticed it happened to me, but restarting Steam returned the counts to normal.

I can confirm all of this as well. The bug goes away if you restart Steam.

I know a friend who fell down that hole. It wasn't pretty.

Huh, that's weird. I've somehow managed to cram 14 hours of Ace Combat: Assault Horizon into the 1-2 hours I played.

Seems like it's adding 12-13 for me.

Are you guys in the Steam beta? That could be the reason why. I've noticed that the hours go up for every hour you have Steam on. They don't get recorded to the servers, and when you launch a game or restart Steam the hours would reset to the real time.

It's adding about 193 hours on to my games right now.

Yea, I've had it too. I'm in the Steam Beta, so it's probably something to do with that.

@butano: @thunderslash: I'm not in any beta and still have the issue, so it must be something else.

OH good, I'm not the only one. Thought I was going crazy.

I don't know what you guys are talking about. I've totally played 226 hours of Portal. That game is difficult.

Yeah I was wondering why 80% of my games installed said that I had played 24 hours.

O_O Shit, I just realised this has happened to me. Although, come to think of it, maybe I really did play 56 hours of Gone Home.

Well originally all my games seemed to have an extra 50 or so hours play time added to them, but I just checked again and it actually seems to have gone up to an extra 75 hours. So yes.

@beachthunder: Only 56 hours? Time's a-tickin' for next year's EVO, y'know... I hear there's a huge cash prize for the player who can fully deconstruct the ludonarrative dissonance inherent in Gone Home without breaking their "looking at VHS tapes" combo.

Every game I have played had exactly 27 hours added to it. Even stuff I only played for 10 minutes.

The Steam Beta update from October 24th addressed this issue:

• Fixed issue with ever-increasing playtime for games that aren't running

Source: http://steamcommunity.com/groups/SteamClientBeta#announcements/detail/1948098256807606776

Mine goes up by one hour every hour on all games that I'm not currently playing and then resets when I restart Steam.

Mine fluctuates wildly. Even though I've completed Castlevania: Lords of Shadow only recently and distinctly remember the hours being around 30, it now says 114 hours, which is way off base.

Yep you just need to restart steam and it'll be fixed.

Apparently I played Binding of Isaac for 8 minutes. That's just poop.