Any Problems with TAGS?

It is very strange, of late I seem to be having problems with the Tags I create for my posts. I will say create a post on downloading torrents and create the tags "downloading, torrents, speed, peers, clients" and insert them, without the quotation marks into the Tags textbox.

Sometimes all is well and I get the individual tags working, only to find a day or two later that they no longer are individual tags, but all been merged into one long tag with an underscore replacing the comma and space. So my new tag looks liks this: downloading_torrents_speed_peers_clients.

Clearly, this is no use and totally ruins the purpose of tags and tag clouds! At other times, the tags fail from the very instant that the post is published. Has anyone come accross this problem, or is it just me and something I am doing? I have also tried the right click "tag" option; even those created by the software do not seem to work.

Any suggestions would be appreciated.