Version:           3.3.2 (using KDE 3.3.2,  (3.1))
Compiler:          gcc version 3.3.5 (Debian 1:3.3.5-8)
OS:                Linux (i686) release 2.6.11wheee

From RFC 1866, about radio-buttons:
---
8.1.2.4. Radio Button: INPUT TYPE=RADIO

   An <INPUT> element with `TYPE=RADIO' represents a boolean choice. A
   set of such elements with the same name represents a 1-of-many choice
   field. The NAME and VALUE attributes are required as for check boxes.
   Optional attributes are:

    CHECKED
            indicates that the initial state is on.
   At all times, exactly one of the radio buttons in a set is checked.
   If none of the <INPUT> elements of a set of radio buttons specifies
   `CHECKED', then the user agent must check the first radio button of
   the set initially.

   For example:

    <p>Which is your favorite?
    <input type=radio name=flavor value=vanilla>Vanilla<br>
    <input type=radio name=flavor value=strawberry>Strawberry<br>
    <input type=radio name=flavor value=chocolate>Chocolate<br>
---

Notice especially the following:
---
If none of the <INPUT> elements of a set of radio buttons specifies
   `CHECKED', then the user agent must check the first radio button of
   the set initially.
---

As far as I can tell, Konqueror does not comply. When no radiobuttons are default, all of them are checked.