A client of mine is currently experiencing trouble with adding image captions via the IE7 browser. I tested this myself and I also experienced the same problem.
Upon clicking the "Edit Image" button, the "Edit Image" modal window appears. I'll type a caption and click "Update". The window closes, but alas, no caption. No default gray caption box -- nothing when I preview, and nothing when I publish.
Everything works perfectly in Firefox and Safari.
Is anyone else experiencing this problem? Anyone have a solution?