This paragraph is defined as follows: font-size:1em; line-height:1.5em;. When I choose to increase the font size [Windows CTRL-+] as displayed font size changes, and the line height should follow. However, what is seen happening is that the line height remains at the originally calculated line height, causing an overlapping of the type as the font size becomes larger. Thus causing an illegible mess.

The paragraphs is of class mini. It is defined as follows: font-size:0.8em; line-height:1.0em;. As you can see, illegibility happens much quicker.

The paragraphs is of class hardtoread. It is defined as follows: font-size:12px; line-height:14px;. It is potentially a much greater real world scenario for the use of browser based text resizing. Unforunately the problem also happens with fixed units.