Which version of Moodle server are you running (1.6, 1.8, 1.9)? Does the problem happen when the student or teacher tries this on a different machine has not previously seen the page?
I suspect that the problem is a caching issue on the browser that might only happen with certain servers that are not up-to-date, that that is a guess.
Also, try clearing or the cache on the browser or at least refresh the page and see what happens and report the results.
--Gary
Assignment
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