OK, so its not exactly a bug. Or actually it is, but a very understandable one...
W3C specifications are for the the [:"blue"] title [/] tags to show as tooltips, not the [:"blue"] alt [/] tags. Mozilla/Netscape is now starting to use the correct way of displaying these, so ALT tags dont show as tooltips. It wouldnt hurt at all to add the title tags.
Example: [:"green"] <img src="smile.gif" title="smile" alt="smile"> [/]
IE is expected to change as well, in the future. Yeah, well, who knows.