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I did upgrade test (I think patch1 > 7.2.1) on xp and linux and I find that the icon of available updates should disappear when you start downloading updates and I am sure that when you are asked to restart ide the icon should not be there. I had problems on xp probabily because I clicked the available updates icon after I already downloaded them, but at the moment I have no time to try to replicate the problem.
I saw that as well, and it's at least confusing ...
Fixed in NB7.3 - http://hg.netbeans.org/core-main/rev/9073ddbccf65