Do you mean that if you issue "yum whatprovides vlc and then a few minutes later
issue "yum whatprovides gimp" the download occurs again?
Not sure if 'a few minutes' but I do remember yum installing something else in the morning, and when I did a yum whatprovides on the afternoon, it downloaded again.
This is a major time waster. For starters, if I do a "yum (any operation other than install)" then nothing will break if the updating of repo indexes is SKIPPED ALTOGETHER.