(The following is probably also true for Mac OSX's Safari web browser since it uses the same code.)
Konqueror has buggy CSS support. This is not very special since all browsers fail to support CSS fully. However its kind of failure makes it impossible to work with demanding CSS code optimised for Internet Explorer and Mozilla's Gecko engine.
The exact problem of Konqueror is that floats (tables and figures) are overprinted by the text that is supposed to wrap around them.
In short, you have two possibilities: Ignore Konqueror and its users and wait for a better Konqueror version, or use the css-mode XSLT option with very-careful, see Further XSLT parameters. For example,
tbtohtml mybook css-mode=very-careful