En-RAGED

So I've got my little habit. Around 2:00 in the afternoon, when I'm having trouble figuring out how I'm going to survive for the rest of the day, I take a break and go grab some coffee. Coffee at work means the Flavia machine. I grab a cup, go to the freezer, take about 4-5 ice cubes, load up the Flavia with a Sumatra packet, and in less than a minute, I have a nice, strong, ice coffee. Well, it's nice enough anyway, and it's free. For the past few months, this has been going well. Lately though, I've noticed little things that are making me a little suspicious. My Sumatra is being consumed at an unusual rate. I'll climb up (on a chair) to grab the cardboard box with the Sumatra packets, pull down about 20-30 of them, and put them in the drawer. The next day, they're all gone. This has happened for about 3-4 days in a row. Somebody's fucking with my fucking Flavia fix. My guess is that some selfish (and apparantly not very resourceful) person is taking the Sumatra packets back to his or her desk. Either that, or they are deliberatily trying to drive me crazy. I don't think I'm being paranoid. Not sure what I can do about it though, unless I'm willing to do a stakeout. Any ideas?