Webpage Question Mark Bug
The more common question mark bug is just the opposite, as simulated by the other writeup on this node (in I'm and don't, or I?m and don?t as they appear on my screen). Microsoft software has an annoying habit of replacing your single quote marks with some high ASCII character which a few programs like Microsoft Word recognize as curly quotes but other stuff, including web browsers (sometimes even including Internet Explorer, depending on the font used to display the text) don't recognize, as it's not a legal character in an HTML file. As a result, the browser displays the ? character in place of the offending one.
The above writeup actually has real question marks in those words, so they will look like question marks on any browser. Thus, it's an ironic illustration of the real question mark bug, while the writeup has the description backwards and the cause attributed entirely wrongly.