selecting a fb account to share a photo doesn't work

Using rtm 241, I've a fb account configured and access auth for fb and fb photos
- open gallery
- select an image
- click on the top-right menu
- select share
- click on facebook

a "Select account" list is displayed, but selecting my account (which is the only listed/configured) doesn't work

the facebook webapp log has

"../../../../lib/SignOn/authsessionimpl.cpp 184 errorSlot QDBusError("com.google.code.AccountsSSO.SingleSignOn.Error.PermissionDenied", "Client has insuficient permissions to access the service.Method:getAuthSessionObjectPath")"

Syslog has

"apparmor="DENIED" operation="connect" profile="com.ubuntu.developer.webapps.webapp-facebook_webapp-facebook_1.0.26" name="/run/user/32011/signond/socket" pid=9649 comm="webapp-containe" requested_mask="r" denied_mask="r" fsuid=32011 ouid=32011"