hmmm, jette dreamweaver (quel nom prétentieux quand j'y pense ...) par la fenêtre. je n'ai jamais utilisé ce truc, mais c'est clair qu'il ne respecte pas le standard :
http://www.w3.org/TR/REC-html40/present/frames.html
16.2.1 The FRAMESET element
<![ %HTML.Frameset; [
<!ELEMENT FRAMESET - - ((FRAMESET|FRAME)+ & NOFRAMES?) -- window subdivision-->
<!ATTLIST FRAMESET
%coreattrs; -- id, class, style, title --
rows %MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 row) --
cols %MultiLengths; #IMPLIED -- list of lengths,
default: 100% (1 col) --
onload %Script; #IMPLIED -- all the frames have been loaded --
onunload %Script; #IMPLIED -- all the frames have been removed --
>
]]>
Attribute definitions
rows = multi-length-list [CN]
This attribute specifies the layout of horizontal frames. It is a comma-separated list of pixels, percentages, and relative lengths. The default value is 100%, meaning one row.
cols = multi-length-list [CN]
This attribute specifies the layout of vertical frames. It is a comma-separated list of pixels, percentages, and relative lengths. The default value is 100%, meaning one column.
//
tu peux essayer de ne rien spécifier (ie juste <frameset><frame ...) et voir comment dreamweaver réagit.