I only seen that happening for a split second. After that, both IE8 and 9 overwrite the text ‘We punch, stamp, etc.’ with the image of the other slide.
IE11 and to a lesser extent 10 are indeed reliable, but IE8 and especially 9 are still widely used. Also, the majority of the reported errors concern IE proprietary CSS. It would be much more convenient if the validator would separate those “errors” from the real errors (which there are a couple of as well). And it would be much fairer as well, because why should CSS with -moz- en -webkit- prefixes be valid, and IE proprietary CSS not?