This issue affect both HTML and Flex client of vCenter administration. Any recent task that is either running OR completed doesn’t visible in recent task tab. At the same time we can ongoing task from monitor tab (Monitor\Task & Events \ Task)
This issue happens because of browser cache issue. cleaning the cache & restoring browser setting to default should solve this problem.
For example, for google chrome following steps can be carried out:-
Settings \ Expand Advanced \ section Reset and clean up then Restore settings to their original defaults