It is never pleasant to return to your office to find that you are in a game of corporate musical chairs and the music has stopped. Although it is not a pretty picture, you should look at the big picture to determine your next step.
On the one hand, it is obvious that this chairperson interrupted your work and generated stress for you. As a result, you need to do more than tell her you are upset. Let her know that the disappearing chair forced you to waste a good deal of time and interfered with your work schedule. And further, the problem is not only what she did, but how she did it. There was no note, no explanation, and no real concern.
At the same time, in today's flat and open organizations, everything seems to be more fluid, including the movement of furniture. If this sounds like the way that your company operates, perhaps your response could be a little more flexible.
The two of you need to discuss what happened here in the context of your organization. Either way, if there are chairs to be grabbed for future meetings, you can let her know that yours should be removed from the list. With some open communication, it should not be difficult to jointly develop a plan that sits well with both of you.
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