[Vala] vapigen can't find aliased type

[Alberto Mardegan <alberto mardegan canonical com>]

Hi all,
  I'm trying to generate Vala bindings for a GLib based library. I
recently added GObject introspection information to that library, and
here is the .gir file:
http://pastebin.com/76wcPHGj
Unfortunately, the generation fails:

==============
mardy devel:/tmp$ vapigen --library Signon Signon-1.0.gir

** (vapigen:24519): CRITICAL **: vala_code_node_get_attribute_string:
assertion `self != NULL' failed
[...cut on many other critical warnings...]

Signon-1.0.gir:478.79-478.79: error: The type name
`IdentityReferenceAddedCb' could not be found
                  c:type="SignonIdentityReferenceAddedCb"/>

      ^
Signon-1.0.gir:535.95-535.95: error: The type name `IdentityRemovedCb'
could not be found
            <type name="IdentityRemovedCb"
c:type="SignonIdentityRemovedCb"/>

                      ^
Signon-1.0.gir:557.83-557.83: error: The type name
`IdentityReferenceRemovedCb' could not be found
                  c:type="SignonIdentityReferenceRemovedCb"/>

          ^
Generation failed: 3 error(s), 0 warning(s)
==============

Since I've just studied how GObject introspection works, it might as
well be that the introspection data is not correct. However, the
g-ir-scanner tool reported 0 warnings, so I have no clue on what could
be wrong.
You can see the code of the library here:
http://bazaar.launchpad.net/~webcredentials-team/opensesame-libsignon-glib/trunk/files/head:/libsignon-glib/

Could it be that vapigen doesn't support aliases of callbacks?
(all of those 3 errors refer to callback function types)

Ciao,
  Alberto