I see the same problem (with portal 2.4).
I have opened a JIRA :
the PortalMetaData() code look strange.
but I recall that there is something about the available portlet mode and/or window state in the portal definition.
I mean, may be those meta data are what the JSR-168 say to be the basic, by default, modes and states.
and the "supported" states are defined somewhere else.
anyway, the portal does not warn if we ask for a state that is not supported.
and also the icon should not be shown...