I noticed today, after following a link on my site that had a PR of 4, it was suddenly a 0. Confused, I looked at the address bar and the page named "uBid.asp" was showing as "ubid.asp" (a link typo). When I refreshed the page changing the lowercase "b" to an upper case "B", the PR was again a 4.

We all know the browser ignores case, but does G? It seems the toolbar PR views the pages as different. Odd huh? Try this with your own pages in the address bar and you'll see.

Nope I see the same PR for the domain name in caps and small. Also files I am on Linux server and so typing in caps gives Not found so could not test.

Never heard such kind of thing.Really odd

Yes it is perfectly possible and does happen BUT you will only ever see it occur if you are hosted on Windows.

To a *nix server ubid.asp & uBid.asp are different pages because the underlying file system is case sensitive, and because of this the SEs do no case transformation on URIs so the same will apply to ubid and uBid.
Windows servers are case insensitive so for a request for either version would return ubid.asp or any other case variant of the same letter sequence.