Whiteboard option unavailable for some users

If it only happens with Google Talk accounts, it may be a bug in the Google Talk service. Can you confirm this? Or does also other accounts have this issue?

Do you mean that the "Whiteboard" popup menu entry is grayed out.
The code looks something like this:

     if {[::Roster::IsCoccinella $jid3]} {
  lappend clicked wb
     }
...
proc ::Roster::IsCoccinella {jid3} {
    upvar ::Jabber::jstate jstate
    upvar ::Jabber::coccixmlns coccixmlns
    upvar ::Jabber::xmppxmlns xmppxmlns

    set ans 0
    if {![IsTransportEx $jid3]} {
 set node [$jstate(jlib) roster getcapsattr $jid3 node]
 # NB: We must treat both the 1.3 and 1.4 caps XEP!
 if {$node eq $coccixmlns(caps)} {
     set ans 1
 }
 # node='http://coccinella.sourceforge.net/#0.96.4'
 if {[string match $coccixmlns(caps14)* $node]} {
     set ans 1
 }
    }
    return $ans
}

I have checked it with jabber.org and the same thing happens.

Looks like it happens when I just sign up as a new account on any jabber server and then add a new contact. Sometimes, the "whiteboard" option is grayed out for that contact. In a day or two, the option appears. So far it hasn't disappeared after appearing once so it isn't that big of a deal. If that happens, then we have a serious problem but not seen so far (thank god! or should I say thanks Mat :) )....

But it does make the software look amateurish. Maybe it is something to do with the way Coccinella is polling the jabber server and then seeing if the server will support the protocol to run the whiteboard. But I am just speculating here.

I have been trying to reproduce it be registering a new account on my
own local jabber server (ejabberd) but it works each time. I am using
a custom element in each presence stanza sent to help identify the
coccinella client which looks like:

SEND: <presence <email address hidden>/Coccinella@linux'
<email address hidden>/Coccinella@Mats-Bengtssons-dator' xml:lang='en'>
   <c xmlns='http://jabber.org/protocol/caps'
node='http://coccinella.sourceforge.net/protocol/caps'
ver='UxStojoiBs0VDfi5otng8zStOmg=' ext='activity geoloc iax mood nick
voip_h323 voip_sip voipgm2 whiteboard'/>
...
</presence>

where the relevant part is the caps element, <c .../> and its node
attribute, node='http://coccinella.sourceforge.net/protocol/caps', You
could try to have the xml console open, menu Info/Debug and see if you
receive such an element.

There have been a lot of discussion going on regarding the caps
elements (XEP-0115) and I haven't followed it lately. It has changed
back and forth which makes it impossible to stay tuned. Perhaps they
have done something awkward so it is filtered out by the serve
somehow. I will test with jabber.orf tomorrow.

I failed to register an account at jabber.org since the connection
just closed after 10 secs. Not sure what is going on. However, I
tested jabber.se and that works as it should. I get the full presence
stanza and the new contact is correctly identified as a coccinella.

Sander, do you use coccinella with your gmail account? I usually also not see the whiteboard icon showing up in the roster for you.

No, I mostly only have my mailbox opened.