...
^^ I know that
Well, this never happened to me personally because I'm not using spaces for spacing; I use letter-spacing instead.
I've seen it on microsoft.com when the page layout was broken because of multiple successive spaces (Browser: IE6 & Opera - I don't remember what version I had then)
And happened also when searching the web... (Browser FF and IE7)
When I see a problem on a web page I get curious and I peek to the source code, and sometimes the problem seemed to be those spaces...
It happened mostly when I was resizing the browser window, but not always.
Problems could come up from wrong designed pages and so on...
As I said, it is just a simple note.