IE/Win CSS bug with multiple class selector

The following code speaks for itself:

CSS:

span.melp { color: red; }
span.zwik { color: yellow; }
span.melp.zwik { color: blue; }
HTML:

<span class="melp">a red bicycle</span>,
<span class="zwik">a yellow bicycle</span>,
<span class="melp zwik">a blue bicycle</span>

IE/Win (only tested on version 6) will also apply the last rule on the span that has only class "zwik" set.

Example:
a red bicycle, a yellow bicycle, a blue bicycle

Note that in CSS1 only one classname is allowed as a selector, as of CSS2 matching can be done on multiple class-selectors. It may be the case that the latter was just not implemented in IE/Win, so technically this may not be a bug but just another shortcoming of Internet Explorer.